Because Reddit's moderator tooling and accessibility are both garbage. Users addressed this with third party applications. So you'll lose out on some disabled contributors, and moderation will get appreciably harder.
Harder moderation means that moderators are even more overworked and likely to leave. A lack of moderation means giving over the community to the bigots and trolls. Bigots and trolls chase everyone else away.
Reddit's content is mostly from real people, and that's thanks to the moderators. Reddit can only sell its content to machine learning farms at a premium price because that content is mostly from real people. So while the admins are "succeeding" at eliminating third party apps, it's going to make their content less valuable.
Meanwhile, most of the LLM makers are going to do unauthorized scraping of the web frontend without paying a wooden nickel.