The execution is definitely not facilitating that.
As far as the mechanics of the game itself, it seems geared for long campaigns -- things like clans, being able to have children and presumably play as them later, the grindiness of the skill system, the relatively slow burn of gaining influence against the high cost of spending it. Everything in the bones, the skeleton of the game itself, seem set up for campaigns that last a very long time.
But there's just so much missing to make the campaigns last this long, and so many things that are also counter-intuitive to a long campaign. A few examples:
Faction snowballing: We've all seen this to some degree. If you haven't yet, you surely will as you continue playing. Once a faction wins a few large set-piece battles, the faction on the losing end often has a very, very difficult time recovering. I've heard a lot of theories about this and I've got a few of my own. I personally think it has a lot to do with the speed/availability for recruits which significantly hampers an AI lord's ability to get back on their feet once they've been wiped out. Obviously, their AI has a lot to do with it. They shouldn't be sallying out without any troops in their army because they just end up getting captured by bandits which starts a vicious cycle of it happening over and over again.
INTENSE WARMONGERING: The AI doesn't ever seem content with its gains. Whenever I join my faction's army and we start rolling, we take one city and immediately set the objective for the next. We all made jokes about those feasts in Warband over the years but that sort of thing helped to sort of soft reset campaigns and get everyone back to doing normal things. In Bannerlord, you just roll from castle to castle, city to city, and if your faction's army is big enough, you roll right through them without difficulty.
A Lack of Intrigue: This one is, I think, very important. Outside of the occasional vote for a castle or some new lawful provision, there is very little intrigue within factions. The absence of intrigue between lords is a major blow to fracturing the power base of factions. It turns them into monolithic juggernauts that win hard, or lose hard. And it leaves very little to do other than steamrolling through castles. I think these last two go hand-in-hand and maybe the warmongering is part of TaleWorlds' plan to cover for these missing features -- I don't know. But I miss denouncing lords, getting into duels, trying to provoke wars on border skirmishes. Now, the wars just seem to start without provocation and without any real explanation. The game loses a lot with these things being absent.
A Lack of Patrols: There just aren't any faction patrols anywhere on the map aside from the few minor factions active. I guess you could also call this 'too many bandits' but bandits are also very important to facilitating early game which, again, might really point out the grindy skill system as the largest detriment here because you absolutely need to fight bandits constantly at the beginning of your campaign or else you'll just never get anywhere. But I think adding some faction patrols around castles and urban centers would do a lot to, hopefully, prevent the AI lords from sallying out without any armies and just instantly getting captured. It would help to just improve the AI of those lords but: why not both?
The ARMY Feature: And finally, and I think most importantly, is the system of joining these massive roving armies prowling around the map. This feature seems absolutely worse in every single way than the Marshal system from Warband because there's just no give to it, no elasticity or flexibility. When a Marshal called an army, it would lead to these gigantic roving bands of multiple lords and their men storming through the map, YES, but a few of those lords would always bleed off to chase bandits, or follow a caravan, or something. There was a chance that steamroll would lose its steam. In this Army feature, it seems to happen a lot less. People join a gigantic army and they just stick together until it dissolves which leads to 900+ troop armies just steamrolling around the map and given the grindiness of the skill system, and of the renown, when am I ever going to be able to stop that sort of thing on my own? It just seems impossible. You can either run away, conceding your castles, or try to form a bigger army and hope you win. And when these gigantic armies collide? The winner continues to steamroll, the loser finds his faction utterly decimated due to the other problems listed above. This is breaking so many campaigns right now because the balance is just abysmal. Everything centers around these gigantic battles and once they're done, the war is basically over. Is this more realistic and historically accurate? Yeah, I suppose it is. But it's not the best for gameplay at all. The stakes are too high in these confrontations and a faction's life or death is decided in them with very little chance for them to recover.
The game seems to want me to play for a long time but it also seems to undercut that from happening. Even if the player kingdom system was full and finished, there would be nothing to do but fight against a gigantic monolithic faction that had taken over the entirety of the map once it had steamrolled everything else. And that would ultimately come down to encountering these massive armies and either winning or losing against them. Once someone had won or lost that encounter, the outcome would be academic as things stand due to the game's other issues.
There are a lot of small tweaks that can greatly improve these things but I fear that for the time being, every campaign is going to feel fairly cookie cutter, just with some random elements about which faction attains supremacy and starts to snowball first.