It's simple, the Yorkdale one may be the largest, but they're not using the 3rd floor. So everything has to be cramped together on the first two floors. They should have used the 3rd floor, in my opinion.
Yorkdale is only 2,000ft2 short of being the largest Simons in the Country at 118,000ft2, Edmonton and Carrefour in Laval are ~120,000
(TEC is 112,000) (Square One is 113,000)
Its temping to go larger, and if the crowds are sustained, who knows.......
But.... Simon's growth rate has been phenomenal and its very capital intensive. They've taken some pretty big risks as it is, and they, and their landlords don't want to be burned by them over extending themselves.
Simons so far has stuck to its proverbial knitting, not adding additional categories beyond fashion and limited housewares/furniture.
No toys, no restaurant, no electronics or sporting goods or appliances.
I don't know if they will ever aspire to be 'The Bay' if more successful; it would be a big reach. But some incremental growth at their largest stores to say 130,000ft2 is very plausible.