Kids today probably would enjoy the old PPG. I mean, Nickelodeon still airs old episodes of SpongeBob, and they air reruns of Drake and Josh on Teen Nick. I watched those shows as a kid, and now my younger niece and nephew watch them too. They don't care that it's old. When I was a kid I watched a lot of reruns of 90's Nick shows. The age of the shows never even occurred to me, I liked them just as much as the newer stuff.
My only guess is that Cartoon Network has Boomerang, so that's why they don't want to air the originals on their main channel. In that case, they should just work on new content, and leave the classics alone.