Earlier quoted context omitted.
Counterpoint, some doctors will zoom in on the most likely problem and misdiagnose. This is in part due to pressure on the health care system (where I live anyway); you can only get a GP appointment for 10 minute blocks, which really isn't a lot. But when a 30-some year old shows up at a rheumatologist with joint pain they will likely go to unusual (at that age) but not unheard of rheumatism/arthritis, not hypermobil…
I think endometriosis is common enough that it would be caught earlier ("Oh, does your joint pain get worse right before you menstruate? Tell me more"), but your point is reasonable. I counter with the platitude that common things are common - especially in fields like primary care, the amount of wasted effort one would expend in pursuing unusual explanations for every presenting symptom is considerable. We thus have…
E.g., I get the whole "if you hear galloping think horses not zebras" adage, but I guarantee you, if someone comes and says "hey when I was in Africa I saw a black and white striped animal galloping really loud", I bet you an uncomfortably large percentage of the "horses not zebras" crowd would still favour a horse over a zebra diagnosis, despite the overwhelming posterior.
Combine this with our (otherwise reasonable) tendency of avoiding the information bias of seemingly unnecesary tests, and it becomes a big problem, whereby uncommon conditions are treated as common, thereby often escaping detection altogether, and driving down their apparent prior probability even lower, causing a diagnostic vicious cycle.