My belief is that people who continue to use reddit normally don't really care strongly enough to leave. They are only upset about the third party apps, but not enough to quit reddit. They don't care about wanting a decentralized internet and having a platform for the people by the people. Even the use of the official app isn't even concerns of the permissions that could extract lot of additional data to build a more accurate profile of users to resell to marketers. I believe for them the outrage will pass. In the end they want to keep using reddit and aren't looking to leave. It's just noise in the outrage, but not an actual willingness to follow through.
Your first reply to me questioned my supposition that the shutting down of the 3PAs would lead users to lemmy. Any users. You suggest that users who would use lemmy are already doing so.