One important issue is that if the patch program goes wrong, you can easily end up with customers having broken installations that you can't fix. The patching software is how you distribute updates, so it has to work. So there's strong incentive to deploy simple techniques with fewer failure modes as opposed to optimizing away every last byte of network traffic.

Firefox has historically shied away from complicated patch algorithms for this reason among others. (To be fair, of course, we're also dealing with several orders of magnitude less data than AAA games are...)