The guys that bought the M45, currently use a similar pistol. Through this purchase they get to keep using the same ammo, same holsters, same magazines, many of the same spare parts (admittedly not all of them) and the users and armorers are familiar with the platform.
Whatever their use of this pistol is, and only those using them really know what works best for the task required, they had already come to the conclusion a 1911, in .45 ACP, with a light rail is the best tool for the job they need done. For this pistol purchase, all they really were deciding was what 1911 was the best for their needs.
Your, or my requirements for a pistol could certainly be completely different from what the Marines wanted. You may find a safety too complicated to operate, they may require one. You may need a double column capacity magazine, they may want the slimness of a single column magazine. You may like a lightweight polymer or aluminum frame, they may require all steel construction.