I always thought the concerts were to sell albums.

Usually, yes. At least, that used to be the case-- the point of long hard tours was to increase awareness for the band and to increase the fan base. Tours would often lose money but still be considered a success if album sales went up in the toured markets.

However in recent years, some really big concert tours have been an end unto themselves, with the goal being to make money on the concerts. This is a tricky thing, because I've heard that a badly-attended concert tour can lose spectacular amounts of money very quickly.