The owner Phil Anschultz is a billionaire. He didn't get that way by being stupid. Beckham sells millions of replica uniforms. All the screaming teen aged girls will go out to buy them. They are ridiculously expensive too. I think he sold over 5,000,000 jerseys in Asia when he switched from Manchester United to Real Madrid.
The profit margins on those things are huge. An $80 shirt will probably net them $40 per unit. The Galaxy thinks they will turn a profit.