GRRM's argument, as best as I could understand, was that HPL was poor in part because he allowed people to write in his universe without paying licensing fees. He speculated that, had HPL charged those writers, he would have had more money, hence a better diet and/or access to medical care, and therefore might have lived longer. According to the nihilistic_kid post I linked (not to mention common sense?) there about a million things wrong with that argument, but that was the claim.

It does seem likely that the expose that Lovecraft's universe got through official and unofficial fic is a huge factor in the ongoing popularity of his work. And really, which would most authors rather leave: an enduring creative legacy, or a pile of money for their heirs? (I'm seeing some evidence that GRRM would choose the latter, which might explain some things.)