That was my first impression as well however, after giving it some thought I wish there are more vulnerability trading companies. The point is that currently this business is reserved for government sponsored customers:
According to three sources familiar with Endgame’s business, nearly all of its customers are U.S. government agencies.
Expanding this business to the private sector might have positive effects. Corporations could buy the "zero days" in their own products in order to fix them. To some extent such outsourcing already exists in the form of pen-testing companies, but it seems like a different league.