Constrained supply

But there are empty properties now. There is supply. House prices are too high for all of the property to be affordable. That is because property as an appreciating investment is valuable. You can only live in one house, to buy multiple properties and have that appreciated investment, you are a landlord.

Low interest rates

allow you to buy a property. They allow people investing in housing to buy many. It results in the above.

Banks pushing bigger mortgages

Sure

Help to buy

Allows affordable housing to become an investment. See my first point.

Rich people were losing to much money

Yep, some of those people were landlords who were finding city prices dropping.

Clearly landlord culture isn't the "only" problem. But fuck me it's a big part of the issue.