This may be a risky question to ask, but aren't left-leaning politics (somewhat awkwardly coupled with the more traditionally right-leaning "great man" theory of causation) pretty endemic in even older RPGs? I mean, Dark Sun: Shattered Lands is pretty clearly a mix of environmentalism and poor vs. rich, for example. And Fallout (particularly Fallout 2) makes a point of satirizing right-wing militarism and suburbanism. Almost every fantasy RPG I can think of has had, at some point, some messaging about discrimination and tolerance (Ultima 6 is probably the paradigmatic example of this). Same with bizarre insertions of real-world stuff, like having Bill Gates be a major figure in Arcanum (if only Troika had known what Appleby would become!) or Dan Quayle jokes in FO2.
Is the issue here (1) that the politics are too far left, (2) that the writing is worse, (3) that the gameplay is worse, or (4) that the issue has simply moved from background static to signal due to the years-long GamerGate brouhaha? Or some combination of these things? I'm not particularly interested in Siege of Dragonspear itself, but I am interested in whether there is a shift going on in terms of players' tolerance of messaging in games.
It's a combination of all of the above. But with one important clarification regarding your first point. For me, SJW aren't far left. I always am kinda baffled by US-centric (and nu-Euro too) definition of "left". Classical left ideology was diverse, I mean, if we take even Bakunin and Proudhon - they had way different opinions about what constitutes the anarchy, what role should the state institutes play, if any, in a ideal society, etc. The main unifying factor for all various left ideologies was the idea about ruling class exploiting subjugated classes, and that something needs to be done about it. I'm stating the obvious here, I know, but it's kinda important, because in XIX century and most of the XX the workers' rights really had been in very poor state, there really was class division, subjugation and exploitation. It was blatant, it was in your face, and because of it leftist ideas were so popular, because they answered the real demand in society.
Now - all these factors are still present, but they are way less blatant, and (at least in part either directly because of early leftists' actions, or because of non-leftist government reactions to revolutions and leftists gaining power) workers' rights, women rights and human rights in general become protected and enforced. Most western societies became post-industrial, with functioning social lifts systems. Exploitation of underprivileged is still present, but it's latent, and conducted mostly on economical plane, which is often too hard to understand for your average Joe, especially if Joe can get himself a credit card, mortgage and so on, and fulfill his basic needs. So - for your average trend-follower classic leftism becomes outdated. Not longer it's something cool, revolutionary and trendy, because downtrodden are familiar, boring, and are mostly OK with their place in society. So they need to find some new downtrodden class. Gays, women, trannies, POC (or whatever PC term they are now using for minorities), muslims, etc. Problem is - most of these groups already have gotten their rights, mainstream acceptance and equality.
SJWs though aren't content with equality, no, they need to invent oppression. Most SJWs are from at least middle class, those kids are both privileged themselves, very insular, and not very bright. So instead of tackling many problematic aspects of their respective countries (and there are many, both social and economic) they participate in this retarded Oppression Olympics, where they invent laughable things to be offended about just to feel themselves a part of subjugated class. It's both funny and pathetic.
What riled so many people it's that they used just this tactic in writing for BG: SOD. Forgotten Realms is pretty mild and generic fantasy setting, it's not very realistic concerning peasants, workers, feudals and other classes sets of rights and duties. I'm not surprised by its popularity in USA, honestly, because it's an ideal american everyman setting, where almost everybody can be basically a superhero. Many RPGs are power-fantasies, true, but in Forgotten Realms themes of racial and class oppression, gender discrimination and so on was consciously made almost nonexistent by setting's writers. They wanted to give DM and players fun and colorful world were you kill shit and get epic loot. In Forgotten Realms there's less moralizing than in Dragonlance with its archaic Epic battles of Good and Evil. It's not as deep, philosophical and fantastically diverse as Planescape (or even Spelljammer), it's not a leftist-survivalist dream as Dark Sun is, it doesn't explore (at least not as a main theme) the darkest corners of humanoid mind as Ravenloft does, it's not an exotic setting where you can explore middle eastern themes like you can in Al-Quadim, etc. It one of the most theme-parky settings second edition era, IMO. It just isn't suited for head-on exploration of contemporary oppression themes.
Now, a good DM, or CRPG writer can explore this themes, but making them a) subtle and b) relevant to both setting, and the theme and the mood of the campaign. But both theme and the mood of original BG (especially the first one) wasn't about exploration of class oppression, gender equality and gender politics, LGBTQABBQ rights and complexes, money distribution among downtrodden and so on. So SOD rubs most players in wrong way not because of "leftism", but because the authors' approach was something like this: imagine you plaing an epic campaign in a span of a few years. You have your favourite NPCs, DM provides kick-ass dungeons, sweet loot, great combat, somewhat retarded, but enjoyable NPC drama and nice overreaching story. And then, out of the blue, this campaign goes to another DM, who proceeds with imposing on a bewildered party his view on women rights, importance of pronouns and battling transmisogyny, insists that your sweet loot should be distributed among underprivileged classes, etc, etc. Most tabletop players would quit in such circumstances, only minority, which shares the new DM views, will remain. And that's basically what we're seing here.
tl;dr SJWs are dumb privileged shits, and not "left" in a true sense; Forgotten Realms is one of the most unsuited settings to explore SJW themes, mainly because many of their imagined "oppressions" just aren't present there; SOD shat on both theme and mood of BG's campaign, inserting their favourite themes into narrative without hesitation or even a lick of sense - hence the backlash.
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