These guidelines are set for BROAD populations - specifically very poor and "normal" people have the same guidelines. For poor people, a high threshold is important to "get them in a house" - they might genuenly need to spend 30% of their income on rent or mortgage. For "normal" people, that same percent is "way too much money" for "way too much house".
The result is that normal people get approved for a big fat mortgage. But we don't want a big fat house, we try and buy a normal house, but we really want it so we pay "just a little more than it is actually worth" and drive the price up "just a little".
Of note, FNMA and FDMC adjust their guidelines for high COL areas and some other guidelines. And also, their guidelines have moved over time. Also, it is a generally accepted "fact" that home ownership is good, and poor people should be encouraged to buy a house.