I think that's the distinction that matters. You can collect it, and it stops being sold, now somebody somewhere wants your set in brand new condition so they can play with it, cause well they love Lego's and you've got some rare set they wish they had.

The lower bound for the price of a collectible Lego set is what you could expect when sold solely as a cheaper, slightly outmoded alternative to a new Lego set. That's better than baseball cards and the like, but still easily offset by the cost of storage and handling.

I have Lego bricks that are from the 80's and they snap together with brand new ones just fine even after being used by my parents through their childhoods and through my own

The Lego Group has some pretty tight tolerances for what's acceptable in a brick. For being a toy, Lego bricks are created to incredibly high standards.