The 1911 is not as reliable, and requires more TLC, than many of the options out there. Also, they are paying a lot of money for these guns, when they could be getting a more capable weapon, for much less. Like M2 said, I own a few 1911s (planning on buying another one...or two) but I carry my XD45. I think any one of the following would have been a better option.
FNP45
XD45
HK45 https://pistol-traini...m/archives/4027
SIG 226
Some will say Glock as well...I'm just not a fan.
EDIT: Forgot to to talk about mag capacity. While nothing replaces well placed shots, when bullets start flying, this isn't always a reality. While I love the feel of a single stack, I would much rather have a higher capacity mag.
The M9 is a decent gun...I just don't care much for it and would much rather have any one of the previously mentioned guns.
The term "knock down power" is more of a myth. Here is an interesting paper on the subject.
https://www.firearmst...df/fbi-hwfe.pdf
I like the .45ACP as well, not that the .40 or 9mm are not capable. The SEALs have used the P226 in 9mm for quite a while (although I'm pretty sure they carry whatever they want).