One (FAIR) is lead by Rob Fergus (who? exactly!) because the previous lead quit. Relatively little gossip on that one other than top AI labs have their pick of outgoing talent.
The other (GenAI) is lead by Ahmad Al-Dahle (who? exactly!) and mostly comprises of director-level rats who jumped off the RL/metaverse ship when it was clear it was gonna sink and by moving the centre of genAI gravity from Paris where a lot of llama 1 was developed to MPK where they could secure political and actual capital. They've since been caught with their pants down cheating on objective and subjective public evals and have cancelled the rest of Llama 4 and the org lead is in the process of being demoted.
Meta are paying absolute top dollar (exceeding OAI) trying to recruit superstars into GenAI and they just can't. Basically no-one is going to re-board the Titanic and report to Captain Alexandr Wang of all people. Its somewhat telling that they tried to get Koray from GDM and Mira from OAI and this was their 3rd pick. Rumoured comp for the top positions is well into the 10's of millions. The big names who are joining are likely to stay just long enough for stocks to vest and boomerang L+1 to an actual frontier lab.