They are rare, but if you build a specific toilet targeted for people with disabilities (next to ordinary, simpler, smaller toilets) then you generally try to make it as accessible as you reasonably can and target a wide variety of different disabilities. Such toilets tend to have many adaptations e.g. different controls for faucets on the sink, different handling of toilet paper, different dimensions and spacing, etc.; and yes, for some people a button instead of a knob that needs to be turned is all the difference in the world, as they simply can't turn a knob. For a trivial (but not nearly the only) scenario imagine a person with prosthetic hands, or extremely limited grip strength caused by e.g. some cases of cerebral palsy.

> Is turning the lock really that different to pushing a button?

I don't know what type of hypothetical disability the person above means, but I know the problem of round doorknobs and gloves so I suppose something like that?

But a horizontal sliding lock as seen on many types of bathroom stalls already should be similar enough that anyone who can push a button in the right direction can also push these in the right direction

However, does a mechanical lock glow and look fancy when you can sell your electronic high-tech locking system to the train manufacturer??

There are other benefits to this too. With an electronic lock you can display the state of the toilet to other passengers on digital signage screens onboard the train. You could do this with physical locks but it would likely be more costly.