???
They do all the extra shyt to put together an event, so the boxers can focus on just preparing for the fight.
You mention Al setting fighters up with promotions, but at the end of the day, Al is still responsible for guiding these fighters through the entire process -- for example, there's no way Wilder was ever in charge of setting up a press tour on his own let alone an entire fight card and venue.
Joshua not finna be simultaneously negotiating with the Saudis and Tyson Fury's team.
Etc.
Fighters have enough on their plate preparing for a fight. It's not impossible, but again, I highly doubt a fighter would be able to or even willing to run a fully staffed promotional company. It's just asking for too much.
i mean oscar had golden boy promotions established when he was still an active fighter but im sure schaefer and some others were the ones doing the brunt work of shyt like the bolded