Googling "psa graded 9.6 NES mario bros" turns up some absurd looking dollar values. I can totally see collecting old video game stuff as a hobby when we're talking about things that a teenager can get for free or nearly free. There's just a vast amount of consumer goods sloshing around North America and lots of peoples' aunts/uncles probably have a SEGA Genesis with some games in a cardboard box on a shelf in the basement.

Or for a few dollars/nominal cost. Sort of like the people who are buying and restoring 30-year old i386 gaming PCs for retro stuff, you can find the hardware for free if you talk to enough older people. Or find a way to intercept it before people literally huck it into a dumpster or take it to electronics recycling. Same for some people who luck into getting nice old 27 inch Sony Trinitron CRT TVs for free.

But when we're talking about thousands of dollars or more per unit for a sealed (so you can never actually open or play it without ruining its value and grading) game in a plastic box, that's a whole other ball game...