What's the difference between a screening and a diagnostic colonoscopy, really?

31F. I've been having constipation issues so I was scheduled for a colonoscopy. I went to double check coverage with my insurance and see that a "screening colonoscopy" is fully covered with not even a co-pay because it's a "preventative procedure", but a "diagnostic colonoscopy" counts as an "outpatient surgery" with a significant copay.

But as far as I can tell, there is no difference in how the procedures are performed, and with the exact same equipment. The only difference is the reason for performing the procedures (symptomatic vs asymptomatic)- and a huge difference in billing.

Appreciate if someone clarifies? Seems.... broken?