Why don't they do a monthly unlimited for the basic inside/outside wash?

So I am the one who sales them, I work up front. I dont know why they dont know why exactly have it for that one. But how many times a month are you gonna do your inside?

The Premium Service Unlimited plan is more cost effective for our customers. After only two washes, the plan has paid for itself. It comes with the conditioners and the protection that keeps your paint shiny and clean, as well as the interior clean every time.

I need it done almost more than outside