RT is a propaganda department of Russian government. Most countries do regulate behavior of the agents of foreign governments on their territory.
It is up to a specific government whether they allow another government to come in and for example spread propaganda or mine coal or build railways. Usually there is some reciprocity expected. Russia blocked not only West government propaganda agencies, it is also blocked independent media. So, the West governments are more than expected to block Russian government propaganda operations, especially given that non government information flow from Russia isn't blocked (that would be the censorship similar to that Russia has been doing, and West hasn't done it yet).
It is up to a specific government whether they allow another government to come in and for example spread propaganda or mine coal or build railways. Usually there is some reciprocity expected. Russia blocked not only West government propaganda agencies, it is also blocked independent media. So, the West governments are more than expected to block Russian government propaganda operations, especially given that non government information flow from Russia isn't blocked (that would be the censorship similar to that Russia has been doing, and West hasn't done it yet).