Ashtanga is a style of yoga that consists of a long series of poses that progressively become harder and more acrobatic. The series is so long and challenging that only a few people in the world can do the entire thing. Most practitioners do about one-sixth of the whole sequence, and that takes about 1.5 hours.
On top of that, this practice involves a few other "quirks." First, it is practiced without music, with the sound of one's own breath. Second, every pose is accompanied by a specific direction of the gaze. Third, everyone practices individually, with the teacher only giving adjustments. Finally, the teacher gives a new pose to a student only after the student mastered the previous one. In a word, it is not at all your usual "Inhale love, exhale compassion" mild exercise routine. It's fucked up.
Why would anybody do it? I can't speak for everybody, but here is my reason.
Yoga offers more than just a physical practice — as everybody knows. To me, the key insight that it offers is the fact that you get nowhere by trying too hard. Get too obsessed with the acrobatics and the desire to make progress, and you will hate the practice and drop it. I did that before. Find enough joy in the practice to show up on the mat more or less regularly, and the acrobatics and progress will come on their own.
Practicing only when my body wants to and not setting any goals, I get further in my practice than when I pushed myself to do it six times a week and compared myself to others in terms of form and progress.
Here comes space for a deep philosophical conclusion that you will make on your own.
(My own next place to apply it is to learn to do less in my coaching sessions. Trying too hard is detrimental to my clients' progress.)