Cavalary: Nothing.
Why the heck would I use yet another piece of software when plain regular installers, a regular folder structure and some memory (my own, I mean, not the computer's) and behavior patterns do the job just as well as they've been doing it ever since I started using computers, and also for other things like music, pictures, documents and whatever else? Simply put, with the expansion of data at the exponential rate it's been happening, many people have far too many items to keep track of manually. The human brain is a monster of raw data processing power, but has shoddy input devices and a terribly inefficient data infrastructure. Couple that with memory and storage issues and the brain, despite its incredible processing ability is an inferior machine. When you are trying to manage data on a large scale, such as games or items on multiple services, it can be useful to have a central repository index of all items.
So the short answer to answer your question: Because not everyone has kept their data profile as simple as you have.
