Well, see, first of all, they aren't writing/drawing CP. See, CP, or in actuality CSAM/CSEM (which if you actually gave as much of a shit about this as you pretend to, you'd know btw), requires an actual child to be involved. Not a "LITERAL CHILD" like you probably call every fictional minor, but an actual literal child, as in a living, breath, thinking child who can and will be harmed directly by the creation of CSEM depicting them. Toph Beifong is not and cannot be harmed by people drawing porn of her. Timmy Turner is not and cannot be harmed by people drawing porn of him. Porn of them is not CSEM. And the problem with CSEM (which apparently needs to be explained to every anti ever for some reason) is not what is might encourage people to do or how icky you find, it is about the child who was harmed and if you can't get the fuck over yourself and recognize that your disgust does not fucking matter then it just further proves how little you actually care about this. So, strike one.
Second, you got any other shit you stole from the War on Drugs or Jack Thomspon? "Oh, they're smoking pot, it's only a matter of time before they smoke crack, if they haven't already." "If someone is killing people in video games and enjoying that, it's only a matter of time before they act on those violent urges in real life." Neither of them ever manage to provide any evidence to support these claims and in fact only ever found evidence disproving. What about you? Got any? No? Didn't think so. So, strike two.
Third, that's not how the law fucking works in any civilized society (which apparently doesn't include most of Europe at the moment). You don't arrest someone because "well they might do this thing eventually, maybe." You arrest them for what they have actually done. And I can already see you typing out something like "but what about threats--" they threatened someone. If someone threatens to murder someone else, they get arrested for threatening them, not for murdering them. If you plant to commit a murder, you get arrested for the planning, not the murdering. If you attempt to murder someone and fail, you get arrested for the attempt, not for the murder. The only time you get arrested for murder is if you have managed to complete the murder. Do you see the difference? Someone who makes fictional content cannot be arrested for abusing a child as there is no actual material link between making that fictional content and abusing a child. They cannot be arrested for eventually maybe abusing a child in some hypothetical timeline. They can only be arrested for actions which actually directly involve the planning, attempting, or committing of the abuse of a child. Go fucking watch Minority Report or read 1984 or consume literally any of the hundreds of thousands of other media that demonstrates very thoroughly where arresting someone for something they might maybe do or for how they think will lead. So, finally, strike three, you're out, stop wasting the time of the various departments from individual websites to the actual fucking Federal Bureau of Investigation who are literally begging you to shut the fuck up about drawings.
Oh, wait, but now the BONUS ROUND. YIPPY!
You claim that someone who is consuming porn of fictional minors is "likely to be abusing real kids and should be investigated"? Well go ahead and read through this little collection and see how that "logic" holds up. You sure seem to hold some interesting company and it seems to me like the real indicator that someone is abusing or planning to abuse children is that they talk like you do.