I believe that the requirement for > 30 day leases is also an attempt to block the proliferation of AirBnB rentals, which the city doesn't look favourably upon.
ie) You can't claim your house has been occupied for 6 months because you've had 30 one-week AirBnB listings in there over a year.
from TFA: "Principal homes, as well as properties that are rented for at least six months of the year on 30-day minimum leases, won’t be taxed."
I would be very surprised to learn that Vancouver renters who typically live in units with < 30-day leases turn out to be poor.