Why an ACOG?

[Jaywalker]

My basic question is "Why do door-kickers in Iraq and Afghanistan who mount scopes always seem to use ACOG?" If the USG buys them under contract, then that just moves the question back one step - why does the USG buy ACOGs?

I had an AimPoint red dot on my previous AR and I know it won't do for me - I'm a scope guy.

So, what makes the ACOG good? Is it more robust than other scopes?

I've read the recommended thread and know there are adequate and cheaper alternatives, but I still want to know why people buy ACOGs.

Thanks.