Carmack couldn't tolerate having to accommodate the need to minimize his own programming efforts in order to not shift code too much and unsettle the other companies relying on the same tech. "The work I'm doing now on id Tech 5 is changing some fundamental class hierarchy stuff across all of our resources, and it's the right thing to do. It's better, because of that. It's incredibly painful just doing it in our codebase. There's no way I would contemplate doing that if I had 50 other development teams that would have to go through and make similar changes on there.