With GPL if they want to redistribute they have to, the owner can choose not to take it, but they do have to share it. Of course you can change it and keep it to yourself without sharing but is a tree falls ...
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We're a place where coders share, stay up-to-date and grow their careers.
Do something and show how you did it so others can learn and fix it if something is wrong or even making it better.
They have to share what they did, which is great!, they are making your stuff better, for free!.
They do not have to share what they did. They can share it, and you can choose to ignore it and keep what you built.
With GPL if they want to redistribute they have to, the owner can choose not to take it, but they do have to share it. Of course you can change it and keep it to yourself without sharing but is a tree falls ...