To your first point, it's actually not legal, and possessing even drawn cp has been treated as a similar crime (which imo is incredibly stupid).

In the case of AI, the training data often included real CSAM material, so it's more like I viewed csam (illegal) then drew it from memory (still illegal but less so).

Humans are given the benefit of "I gathered this data and created a new thing out of it" because that's beneficial to humans. I'm not going to say that humans creating something is magically different from how an AI does, but it's training on often stolen data and/or throttling tons of websites to scrape their data against the wishes of the hosters. It's like if I steal a movie and then make my own movie slightly based on it, the problem isn't my movie, it's the process to get to it (and that it's a human who is benefitting from the result).