From arstechnica.com:

Massive was Microsoft's push into video game advertising and, since we live in an ad-filled world and games seek to mimic that reality, it seemed like a good fit. According to a report by Media Week however, the company has long been troubled, and will soon be shutting its doors.

The problem? Microsoft would rather advertise in Xbox Live, where it doesn't have to split the profits with publishers. EA recently pulled its business from Massive in order to sell ads internally. It's not that you will be seeing less advertising in games, it just seems as if those making large bets on in-game ads would simply rather keep larger cuts for themselves.
Full Story: arstechnica.com