Curious about a computer vision ML problem... Why aren't there more apps to teach us dancing?

I am curious about a computer vision ML problem. I understand that there exist many libraries now to detect human poses by detecting our body parts frame by frame. Wouldn't it be easy to compare two people's movements (teacher vs. learner) as a method teach dance? I imagine there should be many similar apps that teach people to do dancing/basketball/volleyball etc...

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So why aren't there more apps like this 'Dance Like' (app developed by tensor flow to teach people …

apps computer computer vision dancing datascience easy human libraries movements people vision