I seem to have the habit of keeping keys even after they don't unlock anything. But the majority of the keys in the picture are actually all from my current apartment-- when we moved in, there were six different locks with distinct keys, and a seventh that we didn't have the key for. So for the first time, I went whole hog with those novelty pattern key blanks and came up with mnemonics for which pattern unlocked which door.

It felt sort of like I was in an adventure game, so that was fun.

So anyway, the answer is mostly "packrat tendencies".