Because It's Cheap

It's cheap on your pocket & health

It requires little equipment and not the "fancy" one but the one that does the job. The job to keep you coming back to it, to use it without headaches, to keep you in shape without requiring ever more money. The practice doesn't allow over training resulting in barely no injuries commonly caused by lack of breadth that leads to a lack of focus that leads to a poor form that ends up in injury

It's cheap on your schedule and your time

It's doesn't require you to spend endless hours at a certain place, at a certain time. Instead requires very little, you can get a good practice in from 15 minutes to 45 minutes and never more. And those minutes adapt to you and not the other way around. Need to do it in the morning? You had work to do and only 20 minutes left for training? You have to stop before the end? Do it, the practice will be there tomorrow.

It's cheap on your effort

Contrary to modern trends, you can't train at 110% all the time and expect to enjoy it, come back to it. You end up feeling soreness day after day, having to convince yourself to go do it and while you do it you are not thinking about the movements, the form, your breath but about how slow the time is going and how tired you are.

Sure there are moments, be it a competition or a challenge or a test in which even a 120% is expected from you but those are rare moments -  for which you progressively train to achieve and overcome, and followed by days of active recovery not another day of the same level of effort - and not the norm. The norm is the practice, the furnace that gives you more than it takes from you, the one that powers you to have a better and more energized day than you would have otherwise.