Yeah, usually it's a refocus thing for me too.
There's so much cool stuff out there, you end up branching out quite a bit, then, for example (like me) you find that you've got a substantial Sideshow GI Joe collection, with a smattering of other stuff that doesn't really "fit", hence why I'm getting rid of most of my Hot Toys figures and only keeping a couple one-off figures that work well on their own (Arnie T-800 and the original Predator). The rest of the stuff doesn't really work in my collection (Wolf Cleaner Kit exclusive, Berserker Pred, another Pred that I got because I was locked into a preorder and Thriller MJ). It's all cool stuff, but if I feel it doesn't really fit I might as well sell it or trade it for something that does, and let another collector enjoy it.
I did the same thing with Star Wars years ago... I had a lot of SW LEGO which I loved, but it was getting to be too much and I loved vintage GI Joe more.