Pay it forward works in real world scenarios because we receive an immediate return on investment. Ignoring karma and whatever other spiritual thing you are into, and the possibility of pay it forward offering a better environment for all we feel good when we do good. Its built into us at a biological level, it facilitates community, language and jolly co-operation.
RE: Why did a post telling people to report bugs make 3,000 USD in upvotes and my actual post about a legitimate security issue that the developers directly thanked me get less than 100 USD?