I worked at Earl's on King St. during its first year in existence (2011-2012) while at U of T and I can offer some points regarding the relatively recent "Western Invasion" within the restaurant business:
1) I know their hiring practices are currently under a lot of scrutiny as are the dress code standards but in 2011, for front of house staff anyways, the hiring process was much more heavily skewed towards the beautiful. Back of house/kitchen staff hiring wasn't as stringent but at the time, the location being the first of its kind downtown, many young people and students sought employment at Earl's. I witnessed managers laugh at various applicants (once they had left the premises of course) if they didn't fit the beauty standards set within the restaurant. One server, having worked there for a number of months and regularly eating the calorically-dense fare, had gained some noticeable weight by the summertime. Upper management took her aside for a "talk" in which she was politely told to shed a few pounds.
2) Alcohol sales were the main revenue generator of the restaurant: As others have mentioned, the food at these places is almost secondary to the overall atmosphere/ambiance of the place as well as the "experience." Alcohol definitely contributes to the club vibe within these chains and is typically a factor in the clientele it attracts. On weekends, the corporate/after work crowd was replaced by tourists and fans coming in for a drink on game day. 2011 sales were somewhere in the range of $12 million and alcohol sales contributed about 65% of that total. I'm sure this trend is evident within many other non-chain restaurants as well but servers and bartenders were always pushed by management to sell more of what was offered on the alcohol menu, especially various seasonal items.
3) The same family owns Earl's and Joey's. With the success of Earl's it was fairly easy for the Buss/Fuller family to expand the Joey's chain into Ontario. Many are unaware that they are both owned by the same family.
4) A lot of the staff were transplants from Western Canada who helped make the transition phase run smoothly. Many are still there today but the same approach was/is used by the other Western chains as well.
Ultimately, their business model has been incredibly successful due to the various reasons others have pointed out. Sometimes the dining "experience" is more valuable than the food itself.