It was a good movie, but I can see why it didn't succeed at the box office. Personally, I don't think historical accuracy (or the typical Hollywood/Broadway lack thereof) had much to do with it. I wouldn't expect huge audiences for a film version of King Lear, either, and Citizen Kane did pretty badly at the box office. The character flaws of great leaders are not going to draw the crowds seen at a competently-made shoot 'em up.
The economics of film distribution have changed. They no longer have the expense of release prints, and there are a lot of screens to fill at the local multiplex. Films that traditionally had no prospects in wide release are less risky than they were - if it flops, just pull it and put the current hit onto one more screen at the multiplex. No doubt it'll earn out its costs on the small screen, and if they netted a few million more on the wide release, they're a few million ahead of where they'd be otherwise.