Those saying it’s an unnecessary announcement are not thinking of things from other’s point of view. While accessibility may be the main reason for the announcements, the “kerb cut effect” very much applies here, where accessibility benefits everyone.
For wheelchair users (especially less manoeuvrable powerchairs) or mobility scooter users, it can be extremely useful to know which side the doors will open, so you can get all the manoeuvring done in good time, before you’ve got crowds of people at the door waiting to get off. Other passengers on the train also benefit from the disabled person being able to get off quicker and without running over anyone’s feet trying to manoeuvre last minute.
Other people who could benefit include blind and visually impaired people, people with prams or lots of luggage, people with anxiety or autism who like to know what’s going to happen next, people trying to be first off to make a tight connection - or, as we’ve recently seen over in Disputes and Prosecutions, sometimes there might be a platform both sides but the doors only open on one side, in which case an announcement benefits everyone.
As a disabled person I wish these announcements were everywhere, they are helpful to many people.