With the results from the Long Covid phase 2 trial, the lack of viable treatments, the huge number of patients willing to jump in a trial and the relatively low cost of a trial (biomarkers, physical and mental acuity tests and questionnaires) this should be pursued. It's a much larger market base then immune activation in HIV and the profit once approved could fund that trial and so much more.
Being a phase 3 trial rather than a phase 2 it would be larger and therefore more expensive than phase 2 immune activation in HIV so it could come down to being risk adverse. It could also be the FDA being dissuasive of any other trial but IA in HIV.