Some don't, and it can make sense. If you rent it out, then you have to be a landlord, which puts you on the hook for repairs, finding tenants, and collecting rent or evicting them. There's always the possibility of tenants trashing the unit to a large degree. Some of these problems become way worse when left untreated for a week, a month, or longer. I can imagine it making sense for foreign investors to leave units empty in these circumstances.
In a similar vein, it's not just foreign investors. It might also make sense to leave the grandparent's house empty while they are in the nursing home if you live further away. If the grandparents don't need to sell the house to pay for retirement, you'd probably come off cheaply enough to leave it empty, pay the property tax and minimal utilities, rather than risk having tenants.
> you have to be a landlord, which puts you on the hook for repairs, finding tenants, and collecting rent or evicting them
I imagine that there are companies that do exactly that for you taking percentage of rent you'd get if you done all that by yourself. I also imagine there are insurances for landlords and/or investors. There's so much money in this when you approach this as investments (as opposed to not renting your grandfather house because it's too much of a bother to clean it out and think about) that I imagine no sane investor lets their property, they just bought to stand empty.
Property Management companies can be extremely inept. At the end of my last lease the property managers for my place were fired for letting the owners family home degrade so far. The property managers then tried to pass all the damages off to my roommates and I, but we had extensive documentation of the existing damages.
Renters, especially in highly regulated cities/states, substantially reduce the liquidity of the investment. In a lot of places, you can't just evict someone because you want to sell, or you have to adhere to a process that can take over a year. An entire housing market can crash during that time.
I heard they(I don't know who--irs? Banks?) are trying verify the money to buy this Realestate is made legally. I don't know how they are going to pull this off. I think it's just posturing.
A few weeks ago, in order to buy any Realestate in the States, all it took was a phone call to the seller's Realtor.
Some mob/drug dealer/corrupt politician guy where-ever, "Hay, by me tat apartment complex in the old U. S. Of A.". Done deal!
(I've always felt you should have to be a citizen of a country in order to buy that land.)