But you have to do that for every similar service and try and match up records. It would be a nightmare. Landlords would also create different companies/accounts to rent out the max nights per year. It's just not enforceable.

The tax office does this for tens of thousands of companies.

It can easily handle at most a dozen sharing sites. And it's trivial to prevent landlords from registering multiple accounts i.e. make sure no two landlords advertise the same address.