A little insight on Vancouver: PRC investment firms decided that the steady growth of the North American real estate market looked to provide great returns on investment. So, these firms started buying up large numbers of single-family homes in Vancouver. I've heard a few reasons for why they chose Vancouver: (1) the large amount of PRC nationals in Vancouver, (2) geographic proximity to the PRC (relative to other North American metropolitan areas), and (3) the closer relationship with the Canadian government (relative to the US).
Now, the investment firms took a different approach. Many ordinary people and even real estate firms will try to rent out their secondary properties, particularly if the property is in a major metropolitan area. Here, the firms didn't rent out the properties for any reason. Their investment strategy decreased the total available housing supply (for anyone, including renters) while demand kept increasing, so the home prices naturally skyrocketed. They sat on the properties and rode the tide.
The issue that Vancouver started encountering was that single-family homes on a regular residential block may be only 50% occupied. The end effect is you'd have families living on a regular ol' city block but with half the properties vacant, which destroys the development of community in that neighborhood. Also, because the Vancouver housing market pricing exploded, property taxes blew up, yet many residents' neighborhoods became a worse place to live. The housing market wasn't growing because of newfound desirability (e.g. Austin) or fresh industry (e.g. Atlanta and entertainment); in those cases, the new economic activity will provide benefit to the community in a variety of ways. The Vancouver situation only benefited the investment firms with no tangible benefit to the community.
Residents became understandably upset. Hence, the empty home tax was passed to disincentivize the investment firms' predatory investment strategy.