If you're as concerned with information control as the Soviets were/are, it makes a lot of sense.

Comrade leader just shat himself to death, or most of the Navy top leadership just died in a single plane crash, or we just blew a nuclear reactor wide open, and it's time to tell the entire country the bad news.

• We need some time to come up with and distribute whatever we're going to tell people
• We can't have some peon at some TV station mention a simple fact that will contradict the official truth
• We can't allow rumors to spread
• We can't just shut down the transmitters because people will assume the worst.
• We probably shouldn't broadcast light entertainment or comedy, that feels tasteless.
• Propaganda reels often have imagery of armies and violence in them, probably don't want those ideas in people's heads right now.
• In fact, let's make sure whatever we broadcast is extremely obviously not news. Something like a symphony or opera.
• We do want to play up the nationalist angle, so let's go with something domestic in origin. So no Mozart or Bach or anything from Western Europe.
• How about Tchaikovsky? The Nutcracker suite. Runs for about two hours.

Makes perfect sense the first time. Peak Russia is doing that exact same thing often enough for the people to catch on. "Oh shit the Nutcracker's on every station, something terrible happened somewhere."