[pzxc]

Or, you know, they could say, "Hey that trademark belongs to us, but we like what you're doing, so here's a free license to use it."

The requirement to protect your trademark doesn't in any way impede your ability to license it to whomever you wish.

(IANAL, TINLA)

[gonzo]

Well, you can't practice "naked licensing".

[pzxc]

Thank you very much. Perhaps I was wrong. This requirement seems to present an ongoing responsibility/burden for the trademark holder, so it makes no sense for anyone to do it.

http://itlaw.wikia.com/wiki/Naked_license

Does that mean places that explicitly allow "fan fiction" derivative works that use the trademark, are placing themselves at risk of losing ownership of that trademark?

If so, that's very disappointing, as it would seem to be suppressing the ability of authors/creators to be generous with their creations.