A big part of racing is marketing and advertisement for the major manufacturers. BMW I believe had a European-based team competing in the WEC already.
RLL likely is the USA marketing arm, that it also costs about $1 million (so I've heard) to field an existing team to race the 24-hour race.
here's an article talking about the logistics of moving a US based team to Europe for the race:
http://sportscar365.com/features/vid...try-logistics/