Indeed. Busking on the street is fine, as you can just walk somewhere else if you don't like it, but on a train you're trapped with them. Pretty sure it's illegal here as well.

There are places where this is common. They hope to get paid (I assume to get them to leave). Sometimes they're accompanied by pick-pockets who pray on the distracted.

Yeah, I hadn't heard any buskers on the Stockholm metro for years until a few weeks ago when a guy I had seen earlier busking, came onboard again with his weird wooden box with metal strings that is played with two hooked sticks and started playing.