I don't know Australia or New Zealand, but in London that is demonstrably not true: The proportion of empty properties in the areas that are attractive for investment is the same as elsewhere, and the proportion of empty council housing is pretty much the same as empty luxury housing. As it happens, most long term empty properties are empty for other reasons, such as waiting for re-development of the property, or large scale renovations and the like, or issues with sorting out ownership following death etc..

Sure, a few are left empty by owners who just don't care, but there's very little indication this number is high. Especially as in most countries there are rental management companies that makes it trivial to rent out a property even if you're an absentee landlord.

I don't know about London, but in lots of these places, occupancy is determined on the honor system. They don't check power/water consumption or lights on at night like other places. In china, you just need to count the lights on at night to see how big the problem is, or peep through the door to see that the unit is still not even renovated. They did a study a while back using power consumption stastistics that was quickly hushed up as a state secret.

In Vancouver, the problem is so bad that local shops are going out of business for popular speculative properties because their just isn't enough residents to use them, even though prices are sky high and the developments are all bought out.

Speculation always drives empty units.

If you’re well capitalized it is often cheaper and less hassle to leave them empty. Renting is a pain in the ass and makes unloading the property harder.