For important reasons. Also why "revenge porn" is now referred to as non-consensual intimate imagery.

Lawyers and courts say child pornography because laws are not restricted to sexual abuse material. Drawn child pornography is illegal in many places for example.

How do they determine the age of a person depicted in a drawing?

Appearing under a certain age is enough.

It’s a witch hunt. Age doesn’t matter. They might say it’s not, it is.

It's the only term I'd ever seen for it, in any context, until the last couple years. And I'm not a 4channer. Pretty sure it's just another euphemism-treadmill thing. (not that I mind in this case, I think the new term's fine, and certainly not worth fighting over)

Like I said, people are unfamiliar with the topic. In the industry, CSAM is the term used.

What's "the industry"? The relatively new industry in moderating Internet communication? I've certainly only seen the term "CSAM" coming from cops and prosecutors very recently, and they're rarely shy about using their jargon in public communication.

[EDIT] I believe you that it's the term in vogue now, to be clear, but I'm skeptical it was as dominant, even if present, until relatively recently. If it was, then that entire world only recently started using it consistently in public communication, certainly. But, again, it's also fine, I don't mind the new term.