My guess is that is is cheaper.
I think there are some strong unions in the US film industry and they set high rates of pay for people who work on films. I guess people in Europe are cheaper.
Many films are made in the UK, a lot of the Star Wars films were made over here, as well as the James Bond movies.
You can often tell if a film made in the UK as many of the minor parts go to UK actors (like in the first Star Wars movie).



