I went into two dealers this week, both are telling me about a year for a frame. When my eyes bulged, the guy said he has a customer who had been waiting 3 years. That is one reason someone might be on too small of a frame.
I used to be 6'4'' but measured recently I am only 6'3'' with 36' inseam (crotch bone to floor) with a 1.04 Ape Index. I'm riding a 58 cm frame with a 396mm reach and 605mm stack, 73 degree seat tube angle, 25mm setback seatpost and a 150 mm stem. It fits on paper or video for the fancy expensive fitter. I got sold that frame size by a shop with a good fitter but it never felt right.
Does it fit on the road? Not really. I dominate the thing. Balance isn't right. Too small. As an example, I have a steep bumpy descent with some corners. It is a handful for many reasons. I recently took out another bike on the same hill, it is more of an endurance frame than a road racing frame. Going down that hill, I thought......man, is this bike slow. I looked down and the Garmin was saying the same 40 mph as would be about the case on the "racing" bike. It was boring. It might be a little big but I only need a 120mm stem on it and the longer wheelbase and trail seem better to me than too long of a stem with my ass hanging off the rear wheel trying to keep it straight on steep bumpy descents. I might be wrong here.