And because the meta for YouTube is to pump out as many videos as possible, so that a channel owner has more 'content' for YouTube to be jamming ads into, from which the channel owner gets a sliver of payback from, there is a constant drive to push new videos out as fast as possible, so anything that slows down publishing new videos gets kicked to the wayside. The channels that use AI narration just push the script through an AI-driven text-to-speech system, and don't care whether it's using the right pronunciation for heterophones (i.e., talking about the bow of a ship and pronouncing it like the 'bow' of 'bow and arrow', when they could go back and tweak the script to have 'bough' instead of 'bow' to force a particular pronunciation, but that's additional work and time), and then just accept YouTube's default captioning because that's easier and faster; adding captions manually would slow down their pushing out slop even further.