Not being awful for years and years would help.
I always say this, Toronto sports fans are the most tortured in all of sports. More so than even Ohio sports fans, Buffalo sports fans, etc etc.
Our last Big 4 team to make the playoffs was the Raptors in 2006-2007(?), and didn't go anywhere. Our last big 4 sports team to win a championship was the Jays back in 1993, and they haven't made the playoffs since (yes I know they are in an impossible division). The Argos last won in 2004, were terrible for years, showed promise last season, and then were absolutely awful this year. If they want better attendance, GET BETTER.
Frankly, Toronto is one of the best sports cities in North America, and by far the greatest one in Canada. Who is the only big Canadian city not to have a team fold? That's right. Despite being terrible, these teams survive because Toronto sports fans have an undying loyalty. Do you think any team in the States (other than the Yanks, Cubs and Red Sox) would still have attendance as good as the Jays if they'd been as terrible for years? What about in hockey? No chance. Even the Habs has dwindling numbers when they were terrible.
Where are the Grizzlies and Expos?
Toronto is very underrated when it comes to sports culture. We have the Hockey Hall of Fame, the only surviving Original Six arena (and that includes the damn Montreal Forum), the stadium with the first retractable roof in the world, that is still impressive over 20 years later. Like I said, underrated.
/rant that I've done about 500 times.