Why does the invoice I received from UKKO.fi not contain the business ID of the contractor?

Contractor i.e. light Entrepreneurs invoiced via UKKO.fi do not have their own business ID. The business ID on the invoice is UKKO.fi's business ID.

Light entrepreneurs do not have a business ID and is not registered in the VAT or prepayment register. For this reason, invoices sent through us have UKKO.fi's Business ID. Light entrepreneurs work like an entrepreneur and agree on their own work with clients.