People on HN seem generally to believe that for any malicious activity you could do with a bug, there's a bidding group of willing buyers somewhere on some darknet site. That's not the case. Random bugs like this may get passed around, but the bugs that command a price all fit a couple specific molds: they're things you can drop into someone's existing operational process.

A Firefox drive-by RCE has some value: many organizations are set up to actively exploit Firefox browsers. So does an iOS jailbreak: lots of people stockpile iOS jailbreaks, for malware implants and for other purposes.

An important common thread among the bugs with liquid markets is that they have a meaningful half-life: once they're burned, it still takes time to eradicate the vulnerable installations. Serverside bugs are fixed worldwide instantaneously. You can see this dynamic in how grey-market payments are tranched.