Because it is probably the best upperbody compound exercise (meaning you train muscle groups) that is known to men. If not, that does not mean you will never how to do a muscle up get a muscle up, it just means you may need to take a step back and build a stronger movement foundation before jumping ahead to more complex movements like the muscle up. If you have your own equipment, you don't have to rely on the gym and you have no excuse to skip muscle up practice. Beginners might find it helpful to use a false grip when performing a muscle-up on a bar.
Practice doing pull ups then and as you do them try to use an explosive motion so that you are 'bursting' up in a staccato fashion. This will ensure that you are targeting the fast-twitch muscle fibres, which are the ones you use in order to create the explosive power necessary in order to perform a muscle up. Ultimately you want to generate enough momentum to carry yourself up past the bar with little effort during that stage of the movement. Muscle is weight so therefore weighing the same is not going to put inches of muscle on you.
And it may not be obvious right away - but all those efficient Burpees you did in 12.1 actually primed you for the Muscle Up transition. The muscle up is basically a pull up followed by a dip and the transition between those two is the most difficult part of the exercise. People who can't do the muscle up are usually either not strong enough or not using the correct technique (or both).
The muscle up is a very hard and a very advanced technique which is why it's so rewarding to perform. Regular people can do a few push ups and sit ups without training but there's no way they are going to do a muscle up without any previous training. Avoid slamming your chest into the bar, but rather pull yourself up high and aim to look over the bar. Focus on technique, muscle ups aren't that hard if you know how to do them but are very difficult if you don't. Practice chest to bar pull ups and deep dips (shoulders go below the plane of the elbow).
Being able to do at least 20 pull-ups is a good per-requisite for a muscle up; dips are also an important exercise for building the strength necessary (dips how to do a muscle up are an advanced exercise themselves, so a certain level or upper body strength is required to do them safely). In the video on the right you can see me doing explosive muscle ups while swinging the legs and creating an S form with my body to help myself with the movement.