The general dynamic of blocs is working against Anwar and PH. The Sarawak based GPS bloc is much more likely to align with UNMO-PAS and/or PPBM. The reason is in Sarawak GPS's main rival are PKR-DAP of PH bloc. So for GPS to support Anwar and PH would make the upcoming 2021 Sarawak assembly election awkward with rival blocs as allies at the federal level. Also Anwar's age of 72 means that if he becomes PM he will be there for a while which make various ambitious MPs of all parties to be wary of backing him.
I mean 72 is old, just less old than 94 (Mahathir's age)
Is Mahathir's end goal to make his son PM?