Dante1969 writes: "Doug, I am fairly certain over the last 35 years there have been many economic good times where developers could have stepped up and built rentals. Why did they not?"
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Because we had rent controls in place.  Even those they were temporarily lifted back in the early 1990's the developers build using leveraged investment, ie mortgages.  Typically purpose-built rental housing is going to have a 20+ year pay-back period, which is why it took more then 20 years before developers started building again... only to have rent control re-impossed.

This isn't just an Ontario thing, the same kind of result has been observed pretty much everywhere rent control has been tried.  And trying to "stick it to the developers" isn't going to make them build more units.