Why would someone install a game without a license

Answer
It's called piracy.

Answer
In general, when someone installs an unlicensed copy of a piece of software, they've done so in order to save money. By downloading the unauthorized version for free (or at a vastly reduced cost) they're declaring that having the product is more important than paying for the product.

Being broke is no excuse to download illegal software. Neither are the arguments that "the internet should be free" or "it's not like software is a physical thing; one more copy won't hurt anyone." Piracy is still piracy, and engaging in it is still stealing, no matter how the thief tries to justify it.