They are known to be the richest club in the EPL, so I don't know why they are pleading for Manchester City to support them by accommodating their players in the flight.
The news about Man United wanting to board a Man City plane for the Ballon d'Or event has become a hot topic of conversation in football circles, but it is clear that The Citizens rejected this request.
However, from several sources that I have seen, currently Man United has reasons.
This news comes at a time when MU management is tightening its belt. Sir Jim Ratcliffe, boss of INEOS, is trying to cut various club expenses.
Renting your own jet is not a wise decision in this situation. Moreover, MU is also trying to reduce its carbon footprint, by finally asking his players to share a flight home from his last international break, especially his Latin players.
Previously, Manchester United management had cut a lot of expenses. Apart from firing hundreds of employees, the contract of the club's global ambassador under Sir Alex Ferguson was also terminated by INEOS.
From the reasons above, in my opinion Man United is not going bankrupt or anything else, but the reason for this policy is not clear, the point is that the MU manager is keeping something secret, perhaps because recently the Man United club has often lost, I think the reason is that managers are reluctant to spend too much money on teams that go to the upcoming Ballon d'Or or managers think it's better to ride, because later they will also lose and it's a waste of spending a lot of money, maybe or for other reasons that we don't know yet.