There are some places in the UK (mostly new developments in London) that have a significant number of deliberately empty investment properties despite the law here making it easy to evict tenants. They are not being used for short term rentals either.

Although the easiest route (no-fault eviction) is being abolished soon, wanting to sell a property remains a valid reason to evict.

Some people just buy property as a speculative investment.

I do not think it is the main cause of shortages in London - that is people buying holiday homes, which are often large and centrally located. London provides a lot (restaurants, nightclubs, gambling, prostitution, financial services...) that attracts people with a lot of money to spend from all over the world.