Left out of the England set-up by new coach Steve McClaren and given only a fringe role at Real by Fabio Capello, Wenger told reporters he believed the former England captain was given little choice for his future.
"I think he was at Manchester United and he was at Real Madrid and (after that) he did not want to go somewhere else, where he felt he was going down," said Wenger.
"I am sure that, 90 percent of his decision is with the national team. I am sure that if he was still with the England team he wouldn't have done it."
He added: "I am not surprised he went for a different challenge, rather than to go down in Europe.
"I don't think he considered a return here to the Premier League. Maybe one year, or two years ago, yes. But now he wants a completely different way of life."
Wenger felt Beckham's stated aim of turning soccer into a far more popular sport in the United States was a tall order.
"America must multiply this by six, seven or 10 if they want to lift their league. One (player like Beckham) is not enough," he said.
Wenger also said there was no comparison in the standard of league football in the United States and Europe, recalling a conversation with France's 1998 World Cup and Euro 2000 winner Youri Djorkaeff.
"I had a chat recently with Youri Djorkaeff one night, when we had dinner," Wenger said.
"He played for the Metrostars in New York. He told me it has nothing (like) the top level in Europe."
However, the French coach believed that, at 31, Beckham's physical fitness would not be a problem in the MLS.
"He has good stamina and he never had great pace," Wenger said. "But he can last a long time.
"Some players take a dip at 30 and then have a resurgence to the top level and play very well for two or three years until they are 34. I have seen that many times."