The impression I got is ROddenberry really liked Myrna Culbreath, so maybe that's part of the reason why she had Trek books published in the past, but not recently?
Myrna Culbreath is 74 years old now. She and Sondra Marshak published educational games based on phonics after their stint with Star Trek fandom.
Joan Winston, who wrote the chapters of visiting the TOS set in "Star Trek Lives!", passed away a few years ago.
I liked "prometheus design" and "triangle," but the phoenix novels not so much. Maybe Pocket books made them take it down a notch more than Bantam did.
It's my understanding that blackmarket K/S "bonus chapters" for all four of their ST novels were available in the "slash" fanfic circles.