It's obvious he's under extreme psychological stress due to his recurring injuries. Why should he go to France, Bordeaux from his point of view? New country, different culture, foreign language, new club.
Also here in Manchester, the doctors and physio know his medical condition. Changing environment is possibly be the last thing on his mind.
He's settled in Manchester: married, has a kid. Why change all that just to play regular football? Because let's be honest, if he goes to France he will get injured.
He has a long term contract. His life will be stable for at least the next 2 years. Just let him. Let him honor the contract, let's respect the man's decision. After 2 years, it's done.
Also, United obviously had money: we just paid 57-ish million for a central defender.