Why do some people get bonus games/codes.

It would depend on where they got the console from. Some places will offer specific bundles that they put together. Or they were sent a console specifically for review and were given extra stuff.

If I may ask, why? That makes no sense to me. I didn't preorder a game so that I get the preorder bonus game at the same time as the original game's release. Do the people who made that idea, understand what a preorder bonus game is?

The codes are to get people to pre-order...typical ploy to gauge interest and get the $ rolling in early. This, along with a "emblem" or some other "pre-order bonus" is how they get everyone hooked in (and, as people continue to get used to pre-order, they
then occasionally fall for those games that aren't worth pre-ordering)

I don't understand why it's so important to some people to get more gamerscore. It's like a bonus to me, something you work at and are rewarded for with an achievement and knowing you got it LEGIT.

The only time I ever, EVER, trade my games in at GameStop is when they're having a 30% or more trade in bonus. I don't understand why people buy games new if they plan on selling it again, do some research to see how much playtime you'll get out of it, if
you don't think you'll play it again then don't buy it, rent it.