To be able to sell it in the future a higher price without worrying about people living there, or having to pay money to mantain a building that is not in condition to be rented.
Right, because a run-down building sells for the same price as one in good shape.
You're just making the bet that real estate value increases faster than the building deteriorates with minimal maintenance. That's often a really good bet.
I don't think that this is the bet. The bet is that the market will not discount the extra repair/maintenance costs that the buyer will have to incur, which is a ridiculous proposition. Speculators gain nothing from letting the property they own rot away.