There's also the backstock of 1911 magazines to support this choice, and the various mag pouches and LBE already configured for single stack .45 mags, and all the marines that already know the manual of arms of a 1911 and won't have to be retrained on something new and different.
I don't have a problem with front-line regular old marines/sailors/soldiers having a $750 pistol.
I don't have a problem with special forces having a $1500 pistol, or using AMU as a resource to build custom quality handguns (even more expensive).
Frankly, this pistol sounds like it's built for a demanding environment and to perform well in it. It costs more than a Glock or Beretta because it's a quality precision handgun that won't rust and will match existing camouflage patterns, will kill better than 9mm, and will not require extensive retraining of all the armorers that will see this firearm.
I think Colt could sell these for $1200 and still make a good profit off it, and they're padding the bottom line due to the man-hours involved in training and logistics for the Corps... but so be it. The product is worth it to the Marines, so they'll take it rather than screwing with something new.