Do you know they didn't?
A lawyer won't generally tell you "Yes" or "No", but will douse it with plenty of "maybe"s, "probably"s, "it depends", etc. It becomes a matter of risk and probability. And if law enforcement decides to take action to get the site shut down and bring people to court over that stuff being hosted here, I doubt you telling them "I do not see any reason why it should matter." is going to convince them to drop the case.
I'm not talking about porn created by minors, I'm talking about safe images created by minors.