Bit of a gamble isn't it?
If they stay, there will be no capital investment. So that outlay of work already apparently worth circa £2bn will cost even more then and be even further behind our rivals (Everton and Liverpool will have huge upgrades by then).
De Gea, Varane, Casemiro, Eriksen, Fernandes etc (many key players) will all need replacing by then. Another huge outlay for the 2025 bidders to make United competitive again.
INEOS already went for Chelsea, Qatar have interest in PL investment United or not. If both are turned away now, likelihood is both will buy into other PL clubs. This means that there's likely 2 more clubs who will be building better squads than us and serious competition to the top 4, and that they won't be returning as bidders for United in 2025.
The debts of.. £800m?... will all be bigger then and probably have surpassed £1bn
They'll have been told all this by their advisors. Bigger debts, worse squad, bigger capital investment required, bigger debts, more PL competition, the current serious bidders won't return.. This is all before we even think about what the fan backlash would be.
Make no mistake, their ultimate goal is to squeeze as much money out of United as they possibly can, whether all at once or over time. If they don't sell now for a World Record fee, there is absolutely no guarantee they are getting more down the road and are risking the possibility they could get much less.