It's the level of commitment. You can start and stop online activities with almost no preparation or planning. When you watch a movie, you have to mentally prepare yourself to be in one spot and paying attention to one thing for an hour and a half. When you play video games, it takes effort to turn on the console or launch Steam / Epic / whatever.
I had to buy a Clicker for college in a day when any number of phone apps, or even the Smart board, would have done exactly the same thing. I think it cost about $150 and the only thing it did -- THE ONLY THING IT DID -- was serve as an expensive and drastically crippled version of Kahoot. Abject waste of money for all parties involved.