system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Banks/Building societies won't provide mortgage on a flat in a building with more than 6 floors in the UK, what is this arbitrary restriction and why does it exist?

As title says, what up with that? 

Edit: thanks for responses. The building society put the policy into effect last year, they wouldn't give me a specific reason but believe as some others have said that they don't think it's a sound investment due to number of flats. You can pay for a valuation but it's 450 quid and has no guarantees were going to go with another mortgage lender.
gpt
There are 2 types of "owned" property in the UK.  Freehold and leasehold.  In a Freehold property you own the land beneath your house.  In a leasehold you only own the actual house.  Now most leases last for hundreds of years, passing through generations of family who pass ownership of the lease onto a family member.  Eventually the lease will run out meaning the person who owns the building has to buy out the lease or surrender the property.  All high rise buildings are lease holds.  Because there is a chance you will lose ownership of your house banks will not offer mortgages on houses with soon to expire leases.  As most high rises were built in the 1960s on 100 year leases it means the risk is far too high for the bank (who would also have to surrender the property to the leaseholder).  It is irrelevant which floor you are on.