Because it isn't designed to improve your skills. The course is designed to make you a pro, period. However, as usual, good instructor trainers could make a difference.
If your goal is to improve your diving, after rescue the best option is likely tech diving, starting from introductory courses (fundie/essential/intro/whatever you like) if your basic skills are not top notch yet.
Cool! I would love to do it but can't
See above: the DM course is not designed to improve your skills. If that's your goal, tech diving is a better path.
If being a DM is what you need to do this, just do it
Good, but really unrelated to becoming a better diver
Because it isn't a course to improve your diving
In your case, it seems you need it. Go for it
Only if you want to first improve your skills, consider an introductory tech course, before or during the DM.
Lastly, be aware of the cheap courses: ensure the quality is very high.
Good luck!