Why on all real estate websites you need to click to show the phone number?

I've noticed that on all real estate websites, any country, in the details page of a property, there's always a button/field that says "show phone number"... and all it takes to see the phone number is just a click! I haven't seen any website where it takes more than a click to show the phone number... no login/signup required, no restrictions such as "first match" (a bit like on Airbnb)...

Seems kind of pointless of hiding the phone number in the first place. Is it just an easy gimmick to track interest? Is it a "manufactured" CTA?