I don't know the economics of it, but I imagine when you pour a bunch of a money into a set, and especially now, when you're storing the entire thing on your own dime between seasons anyway, you keep it there until you know for certain it's never going to be needed.
It was only months at best, but we know that Pearson found use for the guts of the Card Sharks 2001 set and turned a lot of it into Whammy! And Play the Percentages was out of production in 1980, but a big part of its set came out and got a new coat of paint for Nipsey Russell's Juvenile Jury in late summer of '82. So I suppose one of the reasons you keep a set, even if you know that specific show has a low chance of coming back, is to see if you can't use parts of it, at least.
-Jason