They also figure once you start out there with good pay you will become out of touch with the market rate, and they raise you extremely slowly compared to the market, so that by the time you have been there 5 years you are a bargain to them. Most people just don't keep enough connections outside the company and are incapable of moving on.
So they look at the total cost over 5, 10 years+ and hiring a bunch of new grades and training (even paying for grad school) is cheaper for them.
Startups don't have that luxury. 6 months from now, we might be out of funding. And if we care about what happens 5 years from now, we're super rich. So lets hire better people first. And they don't have the luxury of a fixed process and senior engineers to check everyones work.
It is a giant trap for those that aren't aware of it from day 1.
Similar story at petrochemical firms; my dad is a process engineer mainly for PTA- and polyethylene-manufacturing units, and they surely don't expect most incoming hires to know how the PTA synthesis process works, or even necessarily to know what PTA is (it's a chemical used to make polyester). They just expect a general chemical-engineering background; they don't want to have to teach the entirety of what engineering means, what process modeling is and how you might use it, what debottlenecking is, etc., but they don't expect incoming knowledge to be very specific.