Their TSA says the content licenses are tied to Steam. If you're banned from Steam, you lose the legal right to those games:

This license ends upon termination of (a) this Agreement or (b) a Subscription that includes the license. The Content and Services are licensed, not sold. Your license confers no title or ownership in the Content and Services. To make use of the Content and Services, you must have a Steam Account and you may be required to be running the Steam client and maintaining a connection to the Internet.

Suddenly steam games don't seem so cheap. They're hamstrung games compared to, say, back when you'd buy a nintendo cartridge and they'd basically have no control what you did with it then on (such as resell it on ebay or continue to play it whilst simultaneously disparaging them in public).