Those schools have no interest in doing that.
They already have full control of FBS level rules. The P5 conferences can announce, vote on, and adapt/reject rules for all FBS schools with the G5 having no say in the matter.
They already have all the media money. Not only that, the media companies are in so deep they have to keep promoting the P5 gospel for it to be worth the money they spent.
The same companies who control broadcast/cable tv control the streaming platforms that are interested in carrying sports. The stream only companies (like Netflix) have little interest in sports because there is zero rewatch on that library.
They already have full control of the "FBS playoff" and all the fame/money that brings.
They get to pad their records by keeping the G5 at the same level as them.
MOST IMPORTANTLY IT HELPS THEM KEEP THE "AMATEUR" FACADE.
Why would they risk all that, what does forming a professional league get them?
They will probably lose some fan base as it goes from being an "amateur" to professional league. Professional status is where leagues go to be slaughtered by the NFL.
All those amateur that play the games will become EMPLOYEES. Employees have all sorts of protections that student athletes don't. You would also become legally responsible for the injuries that college football players pick up.
In certain states, those employees will get to unionize and collectively bargain. That will kill the smaller programs in those states but give the bigger programs a huge advantage.
The P5 already won. They control everything, get all the money, with no labor to contend with. They are in the position they have worked decades to get into. Yes, some P5 schools will get trimmed. But they still need the student athlete facade, they have repeatedly fought in court to claim they are NOT PROFESSIONAL.