I'm surprised there haven't been any Georgist responses. I think the biggest reason this happens is that in dense urban areas most of these landlords are really

I'm surprised there haven't been any Georgist responses. I think the biggest reason this happens is that in dense urban areas most of these landlords are really speculating on land value. You'd like to have tenants but most of the profits you're going to derive from owning the property are from appreciation of the land value. It's not always worth it to sign commercial tenants to a long term lease and take on the costs of those tenants vs just holding the vacant building until you're ready to sell. I think the best method to fix these issues is to tax the value of land at close to 100%. This forces the landlords to put the land to productive use or sell it to someone else who will.