If they can do that, why wouldn't they?
That it makes it quite difficult for newcomers to get their foot in the door and leads to all sorts of resume shenanigans is not 'their problem'. That's business-think for you :)
Sad thing is - there is no employer/employee loyalty or community, or anything. It's hop hop hop to get your paycheques to where you want them. Since hopping seems to be the only way to up your paycheque and everyone knows that - nobody wants to hire a junior, spend at least half the time training them to be proficient and then they'll proclaim to be intermediate and leave you.
With web dev or mobile dev (only fields I'm familiar with personally), I can also see that the deadlines are very slim. Nobody's ok with a 1 year deadline for a mobile app and that's how long it'll take a junior dev until he/she can ship something half-decent. So...