I don't believe those numbers will ever come close to converging, let alone bounty prices surpassing black market prices.
It seems like these vulnerabilities will always be more valuable to people who can guarantee that their use will generate a return than to people who will use them to prevent a theoretical loss.
Beyond that, selling zero-days is a seller's market where sellers can set prices and court many buyers, but bug bounties are a buyer's market where there is only one buyer and pricing is opaque and dictated by the buyer.
So why would anyone ever take a bounty instead of selling on the black market? Risk! You might get arrested or scammed selling an exploit on the black market, black market buyers know that, so they price it in to offers.
It seems like these vulnerabilities will always be more valuable to people who can guarantee that their use will generate a return than to people who will use them to prevent a theoretical loss.
Beyond that, selling zero-days is a seller's market where sellers can set prices and court many buyers, but bug bounties are a buyer's market where there is only one buyer and pricing is opaque and dictated by the buyer.
So why would anyone ever take a bounty instead of selling on the black market? Risk! You might get arrested or scammed selling an exploit on the black market, black market buyers know that, so they price it in to offers.