Leaving land designated for agricultural uses gets you tax breaks (it's taxed like a farm) until you're ready to develop it.
Anyway, that's outdated. As just pointed out, there's a bunch of townhomes under construction there now as well as a residence that's part of the adjacent Reena centre (which I don't believe is a retirement home, but same idea).
It's actually quite amazing that piece of land sat there so long.
I think to get the tax status, it has to be "farmed" - so a cheap and easy cash crop like corn is common. Until recently, there was land across Steeles Avenue from Shoppers World Brampton still farmed - one property simply a cornfield, the other run by an old couple that sold corn, pumpkins, and Christmas trees depending on the season; he had a few cows and chickens on the property as well. This was surrounded by high-rise apartments, a mall, townhouses, and a subdivision to the south for many years. Development is finally happening there.