Carmack is also generally writing foundations and engines that are reused in multiple games. If it's not readable, it's useless.
Most indie devs are trying to crank out a game fast because they have a vision and/or they just want to sell it while the market's hot. Most have no plans on touching the game beyond maybe a couple tiny absolutely essential bugfixes shortly after release. Writing cleaner code is ideal, but that takes planning, foresight, and refactoring. That's loads of time for solo devs or tiny teams to devote which could be otherwise spent making new content entirely.
Most indie devs are trying to crank out a game fast because they have a vision and/or they just want to sell it while the market's hot. Most have no plans on touching the game beyond maybe a couple tiny absolutely essential bugfixes shortly after release. Writing cleaner code is ideal, but that takes planning, foresight, and refactoring. That's loads of time for solo devs or tiny teams to devote which could be otherwise spent making new content entirely.