If you mean using the normal calling app and instead using WiFi? People still need to call when not on WiFi all of the time. When out driving, walking about the streets, standing in the middle of a field for some reason. Wherever.
Call blocking is done via third party central registries. These aren't tied to governments or the mobile providers directly though like every company that exists within a country will be subject to their laws.
I think you're saying "they want you to use data so lower their prices on data". No shit, that's how everything works. Someone wants to sell you chocolate they adjust their prices on chocolate accordingly. The internet providers for WiFi do the the same for your homes internet connection. This isn't a special realisation, it's economics 101.