You're going to take your laptop with you into the toilet on the train...?
I don't think I've ever seen a human being do that before on a train. Not to go to the toilet, nor to grab a coffee in another car.
You can't be paranoid about everything. My friend in France had put his laptop back into his bag where it wasn't visible and assumed that was good enough, but someone must have seen him do it and just took the whole bag.
You are applying a totally unreasonable standard, to suppose that the thefts were due to unreasonable carelessness. What, do you think someone should take their large luggage into the bathroom too, every time they need to pee?
Talk about victim-blaming.