It's that time of year again. Clients sending me W9 forms.

More than 10 years in the business and I still have a problem with clients requesting that I submit a W9 form to them as if they paid me income.
They did not. They purchased a service. It was a flat rate service. I was not a subcontractor or temporary employee. They did not pay me income.

I know for a fact that they do not send these forms to their hosting company, or domain registrar. So why is it every year at least one client sends it to me?