I think the problem is that the foundation has too many problems. They've been building their house on sand this whole time so to speak. The Sims 4 was not well received on release, and had many features missing that previous games had at launch.
The best thing they did do with sims 4 is that it's more stable, seemingly build to handle plenty of expansions considering how previous sims games all would run worse the more expansions you had installed.
With Sims 1 and 2 it's resolved with computers good enough, with Sims 3 it remains a problem. If sims 3 didn't crash all the time, slow down and have other performance problems, I would never have touched Sims 4 beyond it's base game and would have stuck with it.
There's just no way to truly fix a broken foundation for a game like this, because the problems are at it's core.