Problem with shim apps is, you need access to the API.

With the advent of AI, the socials have gotten very protective of their hoard (not for privacy reasons, but ca$h)

Eg. #Facebook kept moving the API so developers had difficulty to keep adapting.

#reddit made API so expensive that third party clients were priced out.

For a "Universal social" app, that aggregates Facebook, X(/spit), Insta etc ... You need an API and they would cut you off if the aim of the app is to migrate their precious users.