Speaking on the documentary, Beckham described his first year with his new team as a "nightmare".
Beckham, who could earn his 100th England cap on Wednesday night against France, insisted his move to the US was not a form of "semi-retirement".
"I'm passionate about the game, I'm passionate about this move, and I'm passionate about the fact that the sport can grow here and the potential is huge here," he said.
But he admitted the MLS, where he will start his second season on Saturday, will not be transformed within six months or a year.
He said it would take "five, 10 years".
Asked about his injury-laden first season, which saw him play just five games, he said: "It was a nightmare to be honest."
However, he insisted his commercial deals "never" interfere with his performance on the pitch.
"That's one thing that I've always been able to keep separate," he said. "The commercial things that I do, they're always set aside, they're always second to my football... second obviously to my 'soccer' sorry, I'm trying to get used to it."