By releasing an API, and letting third party developers pick up the slack, the community grows and the main company doesn't have to invest as much themselves into this annoying UI stuff. And even if their own efforts are misguided, there are other options, so people stick around. Once they've decided they got all they need from the third parties, and users are too attached to leave, they cut off access. It's a rug-pull from under the people that helped build the community up so I can see why it feels like a betrayal.
While they have technically not 'cut off' access, they chose their pricing for a reason, and it will have this effect. As to whether third party apps are superior, to me that's a side issue - if main-Reddit makes a user-hostile decision, their site and app won't support ameliorating that since it goes against their plans. Third Party apps can and do, which is beneficial to users.