While this would result in graduates who really knew their stuff, I'm afraid the pressure is in the opposite direction. Administrators lean on faculty to increase the institution's "4-year graduation rate". Because legislators lean on them, because the public leans on the legislators. John Q. Public wants what he's paying for, a four year degree in four years, dammit! (despite the fact that an Engineering curriculum really is five years worth of stuff: it used to be here, and still is in much of the world). Given the current huge tuition rates, certainly that's understandable though: if penny wise and pound foolish.
Some people can learn what they need in less time than others. Some subjects are harder than others. But, everyone and every subject unfortunately has to be mashed into the same timeframe.
Of course, why it's ok for the "professional" careers (as if Engineer or Scientist isn't) you mention to require more schooling is a baffling exception. Good for those fields: they get the time to teach stuff thoroughly!