Per connexion would be pretty bad. Per network.
Let’s say you want to set a static DHCP ip from your router. The only way to do so (from the router, I’m not talking from the phone), is by assigning an IP to a MAC address.
If the address is randomised per connection, affecting a static DHCP ip would be impossible.
Another thing a router often has is some sort of dhcp memory. It remembers the ip it gave to a certain MAC address for some time, then when the device connects back, it assigns the same IP it had before.
So if the ip changes each time either the MAC address changes each time (not sure it’s default), or the router has no memory.
So a no-click device hack?