TV isn’t that into it’s own history. The show is over, that sound stage is now available (actually it’ll probably be used by his replacement), and it’s time to move on. One or two things are probably going to some museum but everything else is just in the way.
You’d think though that CBS would have been smart enough to auction things like this off.
I’m guessing there are a few wealthy model railroading enthusiasts who would have had a really nice bidding war to be able to add that bridge to their layouts.