It's so sad to look on that site (and similar ones)
We can't save them all though can we. If we rescue one though when we can then atleast that is one life we have saved.
I think it happens because a lot of children will bug their parents for a hammy for ages then finally they will get one from a pet shop. Then the hamster bites them and they don't want it anymore, or they love it at first but slowly over time they decide it's "boring" and just forget about it. Most of the time the parents didn't even want the pet in the first place so they wont care for it.