The developers are not the problem.  People want single detached housing and are willing to pay for it.   I also live in the burbs, but in an established neighbourhood.  Almost every house sold in my neighbourhood are to "refugees" from Toronto escaping the apartments and attached housing with minuscule-sized lots.
An examination of both prices and housing starts shows that prices for single detaching housing is growing faster than the prices for any other type of housing.  This is a clear indication of a shortage in single family dwellings.  The number of housing starts for single detached housing is significantly lower, both in absolute terms and in relative terms to other housing types across the GTA.  This emphasis on increased density is adding to the shortage of single detached housing.
BTW, the "missing middle" is not missing.  Ms. Burda needs to do her homework.