They make perfect sense to me, actually.
1) You don't want the merchandising to get confused. The reason the Timm-led CG Green Lantern cartoon failed was that the godawful Ryan Reynolds Green Lantern went and killed all desire for Green Lantern toys
2) You don't want some fucktard in animation to go and basically rip-off, even inadvertently, the movie you've spent years developing and get it on screen quicker because of faster turn-around.
John Semper Jr brags about how if it weren't for him using Blade in the 90s Spider-Man series they never would have made a Blade movie. Watch those Blade episodes of Spider-Man. He clearly read and ripped off the movie script, which had been in development as far back as 1992. You have Whistler, who is not a comics character. David Goyer created him for the film. The comics equivalent was a black jazz musician who got killed. You have Blade as a dhampir (although in the cartoon it's because his mother fucked a vampire) when in the comics he was just a man who couldn't be turned into a vampire. Blade uses a sword (an energy sword rather than a katana because muh censorship) whereas in the comics he only used wooden knives. In the episode where he first appears Blade and Spider-Man team-up to stop Morbius from turning the entire world into vampires. You know, exactly the plot of the fucking movie.
Now imagine if somebody actually cared about the '90s Spider-Man series. It might have completely killed the enthusiasm for the Wesley Snipes film if they'd seen the exact same plot with the exact same characters done somewhere else.