Learning is not supposed to be fun. It doesn't have to be actively not fun either, but the primary feeling should be that of effort. It should look a lot less like that "10 minute full body" workout from your local digital media creator and a lot more like a serious session at the gym.

I don’t think the author disagrees with you. Some people really enjoy the effort of a tough workout. But they don’t do it primarily for the fun. Can / should workouts be entertaining? Sure. But there’s a difference between a primarily entertaining bit of content and a primarily workout-oriented bit of content.