From everything that I've read on the subject, the platform didn't exist before Mark's team was involved.
MTGOX was intended as, but never used for, exchanging "Magic: The Gathering" cards because the infrastructure to actually use it as an exchange was never built out. The company didn't pivot from one technology to another -- because there is no indication that they ever had anything more than the domain name in place.
It's a shame a magic card trading site would have turned out better for him.