They have been under a lot of pressure for years to disable e2e messaging because it prevents them from monitoring messages for child abuse. This was a central point of the trial. While they haven't given a reason for the change I think its reasonable to infer it is in response to this pressure.

However there is another possible explanation

> Tom Sulston, head of policy at Digital Rights Watch, said rather than acceding to law enforcement demands, the move was more likely due to Meta deciding against moving messaging on WhatsApp, Facebook and Instagram to a single platform.