Though I don't have any first hand experience, I would guess "scalpers" for vintage Star Wars toys likely did not start to appear until after the "Star Wars" line ended in 1980. With toys now showing up in ESB packaging, there is the possibility that someone thought to themselves, "hey, they're no longer making the toys in this kind of packaging, I bet I can get some good money for em!"
That's totally a guess on my end, just based on the fact that some people obviously had the foresight in 78 and 79 to save toys in sealed and mint packaging. So perhaps some of them thought to make the quick buck with the release of the ESB line.
On a personal note, it wasn't until around 1989 or so when I first saw what we now call vintage SW toys, being sold for more than retail at a comic book shop.