Alexis became the best-paid player in Premier League history when he joined the Red Devils on Monday and Wenger admitted that it was going to be difficult for the 29-year-old to rebuff big-money offers - especially in the latter part of his career.
"Sanchez goes to a great club and has a great contract," Wenger told reporters. "You can understand it when a professional player can combine both aspects.
"He's 29, so it could be his last contract. Financially, it's important."
Despite the loss of the player many considered to be Arsenal's star man, Wenger rejected criticism that he has not been at his best this season due to a lack of effort.
"Sanchez is a great guy and has always been committed," the Frenchman said. “He is a guy who loves football.
“When he’s on the football pitch he gives his all."
Meanwhile, the other part of that deal saw Armenia international Henrikh Mkhitaryan move in the opposite direction.
United legend Ryan Giggs admitted that the Gunners may yet get the better of that swap, and Wenger seems hopeful the ex-Dortmund playmaker can make a hugely positive impact.
"Henrikh can bring quality of creativity, technical stability and experience," he said.
"I believe we lose a world-class player and gain a world-class player.
"Overall I think Mkhitaryan has the qualities to integrate into our game. He has a good team attitude as well. I’m confident it will work.
"He can play in all kinds of positions. He is very versatile and it should help us going forward."
Alexis could make his United debut on Friday against Yeovil in the FA Cup, while Mkhitaryan will have to wait until the Premier League clash against Swansea next Tuesday for his chance of a first appearance.