The problem with increasing house prices and hence the larger mortgages that people take today isn't caused by the people these changed regulations will affect.  The problem is demonstrably offshore buyers.  When offshore buyers were taxed in Toronto, that market went into a tailspin.  

Prices are high due to offshore buyers competing for properties.  A very large percentage of those offshore buyers are buying for cash - they don't need a mortgage.

Why make it harder for every-day Canadian families to qualify for a mortgage?  They will buy fewer homes, thus leaving more selection, at a lower price, for the remaining offshore cash buyers to scoop up.  Perhaps the prices will sink low enough to compensate the offshore buyers for the additional tax they must pay.  The government gets more tax, but Canadian families fail to prosper.  Why would any government sewer their own citizens?

We all know how Trudeau admires the Chinese.