You know, this makes me wonder - is finished main story would be a detriment to the actual production or not?
Think about it this way - CoC2 and TiTS are kinda is similar in model to Games as a Service or Early Access. Game is continuously supplied with new content/reworked and polished in order to keep people playing/eventually finish it.
But like, do they have any benefit of actually finishing it? Unlike Early Access, they get money monthly and not by sales. So they are closer to Game as a Service model, being free-to-play with paying offering you some benefits. This is a single-player experience, so the closest parallels would be... gacha games? Since most of them are PvE only and add story content constantly. Genshin is probably the easiest example to compare, being the most well-known right now. They add major and minor story content once in 40 days and every year release a new chapter of an already laid down story plan. Thing is - there is no way the game is EVER going to be actually finished. There will 100% be new story line after they are done with their original 5 year plan.
However, how will the things go with CoC2? Will they get any benefits from actually rushing to get the main story done and THEN filling the rest of the areas with content? Chances are all it would do is cost them supporters, since the game is, "technically" done. No early access game I've seen put their endings into the unfinished version. Only when the game is actually out of EA does the ending get added. No dev wants to technically finish something that isn't actually finished.
So of course they want to milk it - I feel like it's the most beneficial way of them making the game from the developer perspective, as they can release updates that aren't pushing the game closer to it's eventual finishing line at all. It's possible that, if they rushed the main story and then started adding new content post "release" the game would still be really profitable, I can't really judge, but I can see the devs feeling like there is a finishing line after which their funds would get lower and lower and they don't want to approach it.