One of Phase II's shipboard shows could have been adapted as a 'bottle episode' for TNG, though. I mean, I suppose "The Child" basically is
a bottle episode, except for the special effects of course.
I suspect that the true reason more Phase II scripts were never adapted for TNG was because of the cost factor. I assume the original writers/creators of the scripts from 1977 were entitled to some kind of payment for the reuse of their story? Would it ultimately be cheaper to just get the writing staff to come up with a new story? There were obvious reasons for why they did "The Child" (writer's strike), but it always surprised me that they followed it up a few seasons later by adapting "Devil's Due" as well. Unless Piller or somebody had been reading all the old Phase II scripts, and simply decided he liked that one?