This is because we get a hit to our server even if the screener is off, and it creates massive traffic for us cumulatively. As of now, that's about 480 million page views per month, which takes a fair amount of server infrastructure to support, and of course costs money. So voila, that's how the pricing plan is meant to work - if you send us a ton of traffic, you'll have to pay more, even if you don't have screeners turned on.
More detail: Any page where you place ethnio code tracks the number of views to that page, and counts as a pageview every time someone loads that page. It still counts even if your ethnio screener is turned "OFF".
Note for Enterprise plans - we can roll pageviews into tiers so you can leave Ethnio code live without having to pay for unused traffic. Our goal is to make it as easy as possible for teams to get in touch with their customers, especially without having to hassle internal development resources. Contact us to learn more.