I think they are simply lazy or shite at designing it properly. I am sure with angle changes they can have one without bend tube to accommodate fork crown.
they could, but a number of issues, first kick the head angle out eventually if you make it slack enough no chance of the crown hitting the downtube, handling will be cack but such is life.
Or change the design of the forks, make them much longer with more gently sloping crowns, fit this to a frame and see the headangle kick back and handling go to cack. Or you can shorten the headtube to accomodate the longer fork but you may then not be able to get the bars in the right place, the bearing separation become very small, and the frame looks odd.
IT is all about compromise, the simplest which is what you see is to put a bend in the down tube.