As I understand it, they're simply responding to how they get paid, which has changed over most of our lifetimes.
They're not paid to keep us healthy (as they are at least to some extent in many other developed countries), they're paid for testing, expensive procedures and volume. So they see as many patients as they can and order as many tests and procedures as they can. Like my example in post #1, a doctor spent 5 minutes with me and scheduled a fairly costly procedure, I am fairly certain he'd already decided what he would recommend before he ever saw me.
And malpractice has undoubtedly pushed doctors to test more often than they otherwise might have.
I suspect the health care our military folks receive may be one of the few models left in the US where doctors are paid to keep the troops healthy, not to order tests and procedures.