This article makes some "hand waves" about how understanding of the disease was simplified https://www.vox.com/science-and-health/2017/11/3/16599072/st... but the fact is blocked arteries don't let blood flow.
To be clear though, they aren't talking about ACUTELY closed arteries as in a heart attack or myocardial infarction, when there is a plaque rupture and a blood thrombus that develops to cut off blood supply suddenly. But rather, when blood flow, which has been slowly narrowing over years, starts causing chest pain on physical exertion, when the heart muscle distal to the narrowing is asking for more oxygen than the artery can supply.
We put stents in a lot of these people, because we like to try to help them, but there isn't much evidence that it helps. It may help, but we haven't been able to prove it yet. Or it may help select people, but we don't know which people to select. But many will still keep getting these stents. Medicine is tricky.
On the other hand, studies of procedures are done on very narrow patient populations. Our patients often don’t fit into those perfect boxes. What’s “needless” is difficult. As long as folks get paid per procedure, it adds bias that favors doing instead of not doing.