I don't think he was saying mathematicians don't find it interesting because it lacks sufficiently convoluted mathematics.

Rather a 'true mathematician' (who by definition ignores all practical considerations) would find it unsatisfactory because the problem of finding a way of allowing toilet-less carriages is solved by not allowing toilet-less carriages.

Frankly I think they should have just put the toilet in the middle of the toilet-carrying carriages, but maybe I'm weird.