Because if you don't want what drops for you, you can:
1) Give it another party member.
2) Trade it for something another party member has that you want.
3) Keep it and trade it later for something you want.
4) Sell it if there's an AH-like function in the game.
5) Save it and give it to your Diablo-playing girlfriend for Valentine's Day to avoid having to pay for actual flowers, candy, and/or a gift like the cheapskate you are. (Not referring to anyone specifically when I say "you," btw, except for possibly myself.)