tl;dr: Messenger Lite, Meta’s “less than 10MB to download” lightweight version of Messenger, will no longer be available on Android after Sep 18, as Meta redirects users to the Messenger app. The main Messenger app will also drop SMS support next month.
I doubt that’s actually the reason. This seems to line up with the roll out of end to end encrypted calls through Messenger, at the same time calling is being depreciated on the Facebook Portal device. My guess is either the library is too big or they don’t have the staff working on the Lite projects like they used to. Bulk of the target audience for Messenger Lite would probably be using WhatsApp.
But the team may have been gutted with all the Metaverse obsession followed by the AI obsession.