As someone living in Montreal, I can say that the Expos have been doomed for at least the last 5 years.
First the stadium is nowhere near the core of the city, and it's a terrible baseball stadium at that.
Secondly, lack of ownership. There hasn't been a stable owner since Bronfman gave up the team in the early 90's. Since that bastard Jeffrey Loria left, the Expos have been owned by the MLB. The end result is that no one was putting money in the team and the Expos couldn't field a competitive roster.
Thirdly, none of the past owners have been willing to put money into keeping star players, so as soon as anyone becomes good they get traded away. This means that the team was essentially rebuilding every year.
Lastly, rumours have been that the Expos would be moving for at least the last 3-4 years. Hard for a city to get behind a team that's got one foot out the door already. I've given up on them for awhile already, and I'm pretty indifferent to today's announcement.