Not to start a pie fight (although I love them!) but the Marines chose an 8-round steel pistol that rusts in a marine environment over a variety of polymer pistols that could shoot a decent round and have 14+ rounds in the mag?
It does seem like an odd choice - if they wanted a handgun in .45 ACP, there are much more modern handguns available, ones that are much more reliable, are less labor intensive in terms of maintenance, and that have a higher magazine capacity.