It's more valuable to be in use than to sell it to you. They are very limited on ipv4 space, so the charge is really a penalty for keeping that resource from another customer.
IPv4 allocation limits are still mostly a scare tactic to get people onto v6. I know dozens of people from my webhosting days with /12 and /16 allotments doing nothing that they pay peanuts for. This isn't a unique scenario.
That's not relevant, if I have 10 cars and you need a car ... then all that matters to you is that you need a car, not that I have 10 cars sitting there doing nothing. People sitting on IPv4 addresses don't care but new entrants cannot get new IPv4 addresses since they're all allocated.
