Part of the reason why it's so expensive is because the artists are getting a percentage of profits on top of a fixed fee per performance. They're absorbing a much lower amount of risk than the promoters are.
Add to that the cultural aspect that artists have a stake in making tickets look artificially inexpensive -- no one wants to see Bruce Springsteen "take advantage" of his fans, but if TM does it, then they take the blow even if a cut goes back to the artist/promoter.