While I cannot speak for others, in my instance it is partially due to trying to fill a category. An an example, it has been a goal for me to obtain every kit or decal variant for IMSA GTP, and GTO class race cars. I also have done a similar thing with SCCA club racing subjects, collecting models that could be used in 1:1 builds, as well as generic builds. And while I've been at it, Trans Am subjects, both vintage and more recent.
Also, the IMSA cars, many were only done in resin, thus making them relatively rare. Consequently, when I see one come up on evilbay, it gets followed and bid on.
Just my 2 cents worth.