Nat Gertler has made a chart, and even though his name is not Clarissa, it might just explain it all for you.
Gertler’s chart shows all the movies based on comics properties since 1982 (chosen as a significant benchmark in the “creator ownership era”) and shows that creator ownership did change the equation.
What can be seen is that once creator ownership was on the table, the moviable properties were largely works that creators maintained ownership of. Of the large mainstream publishers that preexisted the change, Marvel and Archie have published no new company-owned properties that have reached the big screen. DC has published four over those 30 years. In contrast, in just the 10 years preceding 1982, Marvel launched 6 purely-Marvel-owned properties that would later become movies, including a couple that were made into movies within 15 years after creation (so it’s not merely a matter that company-owned concepts take longer to reach the screen – although they seem to – that prevents post-1982 Marvel material from showing up.)
Now why this should be…another significant date on this timeline is 1989 when the first Tim Burton Batman film because the fastest grossing film of all time. It was the pre-dawn of the “pre-awareness” model, and although nerd pre-awareness wouldn’t come about until the Internet took control, that loomed even larger in 2002 when the first Raimi Spider-Man movie replicated the effect and became one of the fastest grossing movies of all times. Of course, since then here have been lots of comic-based movies—but exploiting that company-owned back catalog is either all they can, or all they WANT to do.