[imtringued]

It's different, because you are willingly sending a reply to a known UK address.

In the website scenario, there are no physical addresses with a geographic component to them. The physical topology of the network is only known by the operators of the network. Only they know where the routers are physically located.

This means geoip blocking can only ever be done on a best effort basis. Actual blocking can only be done by the operators of the routers, which is why it is unreasonable to expect the website operator to be responsible for perfect compliance.