Because nothing says responsible governance like raising taxes on one of the few parts of the economy that is doing well.

As noted by Messrs. Brodlieb and Kumar in their article, “Ontario raises land transfer tax rates”:

“The tax rate on the portion of the value of consideration above CA$400,000 for purchasers of all other types of property would increase from 1.5 percent to 2 percent. `All other types of property’ include, for example, commercial, industrial, multi-residential and agricultural properties. […]  [T]he increase of 50 basis points for commercial projects will likely have considerable impact on developers, landlords and other commercial property investors. In light of these new changes, purchasers who do not have the protection of the transitional grandfathering (for example, where a written agreement of purchase and sale had not been concluded by November 14) should consider closing Ontario property transactions before December 31, 2016, in order to avoid the increased rates, where possible.”

Further readings:

Jane Helmstadter, “Ontario Modernizing Land Transfer Tax”
and
Vince F. Imerti and Andrew Elliott, “Ontario Land Transfer Tax rate increase and other changes”