There is an active, mature market for IPv4 addresses (just google "IPv4 address broker"), so it stands to reason that there are people hoarding them for speculation.

It's not free money, of course -- it's entirely possible that the value goes down, as things that reduce the pressure on the IPv4 address space slowly come online (CGNAT and IPv6)

That said, I'm a bit confused by this story. ARIN ran out of addresses in 2015, and it was my impression that since then you can't just get IPv4 addresses for free from them, which is why the above-mentioned markets exist. So, how were they able to keep running this scam after 2015?