I don’t think it’s a question of raises, more like they’re just not willing to invest the time.
Most non giant companies don’t have good processes for on boarding engineers so it’s mostly yolo. They want engineers to be productive very quickly. Someone just out of college will likely not have the skills required to drive projects on their own to completion without help/supervision.
Bigger companies have pretty great onboarding tools and processes and dev tools that abstract most complex things away, allowing developers to become productive rapidly. I think of them as factories that can extract the most value out of new grads.
I say this as someone who was a junior not that long ago, but of course my experience is anecdotal so take it with a pinch of salt.