That's because no properties are empty. The owner's nephew, a Canadian Citizen thanks to birth tourism, has the condo his uncle bought registered as his residence.
Converting property taxes to being calculated from unimproved value [0] accomplishes the same goal, while also removing disincentives on development and improvement.
Vacancy taxes tend to only hit the wealthy. There are certainly regressive taxes we should examine (like sales tax on staple goods) but vacancy taxes tend to target high earners pretty effectively.
Taxes are generally a good thing since they allow society to function well.
Richer people own more property than poor people. You're using an old saw that says taxation is worse for the poor but it's not. It's also simple to give breaks for purchases under x dollars or redemptions or for family homes that are occupied etc.
Sure, there are a bunch of corporate people who live in PO boxes in Delaware or Wyoming with no income who own vacant properties. Wouldn't want to burden those poor folks.