Because most people don't want to, (although some are forced to by circumstance,) raise a family in a condo in the concrete jungle.  Imagine getting your kid to hockey practice at 5am by taking public transit.  Send your kids outside to play amongst the needles and the garbage?  Not likely.  

There is a reason that the suburban lifestyle is so immensely popular with families, despite the enviro-nuts and city planners telling us we can't have what we want.  It is great for raising kids and it is a nice lifestyle for adults.  I'd rather mow a lawn than lug groceries up an elevator and along a hallway.  That's why 3 bedroom condos aren't common.  If there was demand, developers would build and sell them in order to make a profit in meeting the demand.