They're arguably the biggest club in the world in terms of revenue and exposure: they'd be buying a brand with worldwide reach and huge potential.True but typically these despot regimes often want a success story (sportswashing) in building a club up - City, PSG, Newcastle.
Utd is a weird one as already a brand name and will cost a fortune to buy.
The prestige is what they'd be buying. Someone who bought Everton would never have that kind of global reach.