>>103166277That's not really as simple as it sounds.
Warner Bros. own (for example) DC Comics and the film rights to Harry Potter, but that doesn't mean they can put out a Harry Potter film that features Batman. It's a question of who else is a stakeholder in a project (which may well be several other major companies, as was the case with the 1960s Batman show until 2014, when a fan resolved it at his own expense). So in our example, JK Rowling hasn't said "yes you may make" a Batty Potter movie, so WB can't make one because there's no contract that says they can.
With Johnny Quest, there may be residual rights issues with the estate of Doug Wildey, there are licensing issues (Warner Bros. Animation is a distinct legal entity owned by Warner Bros., not part of the same company, and the rights themselves are likely held by another series of shell companies to avoid liability problems if WBA or WB is ever sued or runs into financing problems). It's true that WBA appears to have rubber stamped the use of HB characters in ads since the 1990s, but that's a far cry from approving their use in an adult-oriented cartoon. In 2018, more than ever before, there's a real risk of screenshots or animations or whatever else taken from such a show becoming well-known memes, which hurts the chances of getting investors in any potential movie - because studios don't 100% finance their own movies. That's what all those other production companies and producers do.
tl;dr it's more complicated than you think it is