Because I watch the Q&A forums every day here throughout the day. Numerous reports from multiple different people of severe FPS drops with trains in their save down to 20 FPS, time tables broken. Trains kill you when you hop out after manually driving them and won't give you a box and all your stuff is lost, Some people can't get out at all, some people drive to the end of the track and all the trains and cars get "smooshed" together as one vehicle that you can't drive. Train stations don't give the materials back to rebuild if you dismantle em, train cars/locomotives left floating in the air if you dismantle the track they're on and you can't dismantle them or ever get them to go away at all.. etc, etc, it's just a poopfest at the moment in general with trains.