Our recently delivered new aircraft all have ashtrays in the LAVs......
I believe that the thinking on this is as follows...
You may not smoke anywhere. If you do decide to sneak a cigarette in the aircraft toilet, we would rather that you dispose of it in the ashtray than try and hide it somewhere else where we can't find it so easily and where it might set fire to something else that blazes more merrily. We'll still have to do all the usual checks - going through the waste bin and compartments because if you're stupid enough to smoke in the toilet in the first place, you're also stupid enough to do almost anything.