For one thing, we are basically buying used bikes, unless you were lucky enough to buy one to be built for you back in the day. So, there are compromises, waiting for the perfect bike will keep your stable small.
There is a range of bikes that I can fit well, not a big range but enough. Not every one is the same size, nor do they need to be. In addition, I don't set up every bike the same way, especially in regard to seat to bar distance and relative height between the seat and bars. The reason for this is as one ages as I am forced to admit, some days you wake up less flexible, yesterday's position is not good today. The cluster of positions is not that far apart, and having more than one bike to select from makes cycling more enjoyable, better to ride than than not.
I do see often seat angles where I know- a severe downward angle lets say, is hiding a problem, and causing others, the rider will constantly be pushing himself back up the seat, knowingly or not, using more muscles than needed, where he should find a more comfortable saddle to begin with or look at his saddle height and or set back to see why he needs the tilt to be comfortable, but the other variables are just that, adjustments. Way back there were guys in the bike club that I was a member of who swore that the tilt was just going to have to stay there, with enough tweaking, the got more comfortable and performed better, increased comfort gets one farther.