I agree. Multiplayer RTS and then MOBAs which took over the same space are more like sports. That can be enjoyable but it does nothing for single player players, and there is a lot of demand for single player RTS games, like Age of Empires 2, Starcraft, Warhammer 40000k Dawn of War, Stronghold, and many others.
RTS is an easy genre to enjoy, at any level, as a beginner or whatever. You and I know C&C, AoE, WC, SC, etc, are enjoyable as casual single-player games, that children can just pick them up; because thats what people did in the 1990s, before the great amnesia in gaming. Most multiplayer matches are like 'drunken brawls' as someone put it, with no skill involved. I had no clue as a kid even about what unit countered what, etc, never mind anything deep.
There is apparently a perception however, probably born of eSports clips, plus urban tales of how Starcraft was played in Korea, that RTS is a super-hardcore-only genre. People like myself never once bothered to play in a hyper-competetive way; that's just some fringe thing, probably far less than 1% of paying players, but the perception is apparently that 100-APM to 400-APM pros are the normal skillset, at least for online if not SP. In the 1990s we just fucked around. The general casual gamer now apparently looks upon RTS as a formiddable genre, and think that it requires huge management skills and inhuman APM. To beat the AI, you probably don't need any of that, or to play normal multiplayer, maybe just a few minor deeper skills, like knowing build order (which I agree isn't exactly transparent to players). It's a pretty far out notion to us who grew up in the 1990s, to think you have to play like a Korean Starcraft pro, but I can see how a younger person might develop such an illusion.
So
Palikka posted a video above, where I must have seen those demographic stats, citing that 80% never convert to multiplayer, and arguing that most time should therefore be devoted to a good campaign. What I found really resonated to me, is that the guy argues that at some point in RTS history, the genre forgot that it was always primarily a single-player driven thing, for single-player fans. That not creating a beautiful single-player world, companies shoot themselves in the foot. (Like with some other gaming genres).
Westwood knocked it out of the park with their FMVs, their world-building, a setting you wanted to learn about in your own time. After that, I personally think I noticed a lot of RTS games paying less attention to single-player, like the video says. Some of them were at least given less emphasis, rather than an operatic war-story.
I think the clip might be inside that video someone Palikka above, and I think they were specifically talking about Starcraft 2, in that particular case.
4:22 mark on the video. He says that they see about 80% play the campaign, but only 20% "stick around for hardcore multiplayer". Blizzard has a free-to-play model for Starcraft, where anyone can install it, but to get certain features requires a payment. I think the remastered graphics for Starcraft 1 are behind the paywall, but the game is otherwise free.