I am not aware of any countries restricting the use of WiFi on planes (although I suppose it's possible). I don't know if that's what this sentence refers to but there are several countries restricting the use of satellite communications, for example banning them completely on the ground or up to a specific altitude.
Most importantly, several large countries (the US, Russia, China, Australia) require that all traffic originating in their airspace go through a local ground station/gateway to allow for interception (it's called “forced routing”). Qatar Airways (and the satcom operator it relies on) might be unwilling to comply with this requirement and chose to interrupt the service instead.
A comment on this article suggests regulations around the use of satellite communication is indeed the reason behind this clause. It mentions China and India, which is also notorious for its restrictive regulations. In India, you need a special authorisation to import a satellite phone, Iridium and Thuraya are banned entirely.