It's not that they don't understand, it's that they have very limited CONTROL over what happens in other countries.
It happens like this:
A company makes a movie…in this case, Ghostbusters. Now, Hollywood is pretty US-centric, that's no secret, and it was especially true 20 years ago. They only cared about marketing to North America because that's where all the money was.
Once they make as much money as they feel they can by showing the movie in the states, they open up the floor for distribution companies to purchase rights to the movies overseas. Many times this includes some merchandising rights as well, as these distribution companies have to do all the marketing pretty much from scratch, and the licensor can't be bothered to do things over and over. They just take what they can get and write it off.
This is what comes back to bite them in the ass. Once they have sold away those rights, they become difficult to re-obtain. The studio has what they see as a minimal amount to gain, so it's not in their best interest to intervene, leaving the licensee on their own to negotiate any contracts.
The reason you can get the big-name stuff is because they own those characters outright, and so publishing rights are not an issue. But believe me, if Marvel or DC were doing Ghostbusters comics, they'd have the exact same problem…which I would almost bet is part of why they don't really do that kind of stuff anymore.