I feel like Messenger was originally a new front-end for the send message feature of thefacebook.com's social network for college students. It was based on the PHP architecture where all the messages are in a database and you just render HTML to show them.

That grew into the Messenger mobile app. They eventually added private messaging, but it was never popular/defaulted because users expected the chat moles on facebook.com to be able to show the same messages as the mobile app. If facebook.com can't read your messages, it can't show them there.

That era of Facebook was the last shred of respect I had for them, but it was starting to die for me. Now I've noticed younger generations really don't seem to care about Facebook, and friends I grew up with who used to post on Facebook no longer do.

I feel like if e.g. Whatsapp were not end-to-end encrypted, it would have faced significantly more regulatory scrutiny in the EU and other places where it's effectively replaced phone calls and SMS.

Then why end the more insidious route rather than stay the course?

This has always been my assumption as well.

Then why end the feature? Would it not be better to maintain the facade and continue to benefit from it?