I expect that there are myriad "tests" that any/all candidate replacement pistols had to go through...sand/mud/snow immersion, functionality through xK rounds before jam...yadda yadda yadda. Number of parts...ease of maintainability...the whole "Life Cycle Cost" thing. Any 1911 variant (however "improved") has been through and prevailed through this testing for...what? Over 100 years?
But is it the "best?" I know, that's not always the criteria, but in this case, many of those things you mentioned are "better" on other pistols. The 1911 has 8 parts (I think I got them all) when stripped. The Sig or Glock have 5. The 1911 likes to be run wetter than other options for continued reliability (I don't mean how you and I would use it recreationally, I mean in an environment that's not as sterile). There's a well-respected guy online (sorry, I don't know the link) that ran something like 20K rounds through his G19 with minimal maintenance. The 1911 may be able to do that, I'm not saying it can't because I don't know, but just a data point. The argument "it's been working for x years, so why change" can be made for many pieces of gear with stars and bars on the side. Hell, the M1 system is still in limited use today, but that doesn't necessarily make it the best choice (heavy, lots of parts, etc).
I'd be curious to know what the bid would be for all three, broken down per gun. I know DoD does fuzzy math with acquisitions, but the number would be interesting...assuming the other two even competed.
Disclaimer...just so you don't think I'm a 1911 hater:
-My first gun was a Colt 1911 (M1991). I still have it and don't ever plan to sell it.
-I don't find the Glock to be the best gun for me because of fit and comfort. But I do respect it's durability.
-I've carried the Sig (228) operationally a few times and have been very happy. I'd feel pretty confident if I went down with it.
-I've got a crap-ton of rounds through my personal Sig (229) and have been happy for the most part, but have had an occasional extractor issue. Something that can happen even with the Glock, as Bunk has attested to.