IANAL but, if they write software and publish it under a license, it does not restrict their own ability to do anything with the software. But, if they accept a

IANAL but, if they write software and publish it under a license, it does not restrict their own ability to do anything with the software. But, if they accept a contribution under a specific license then that would be different. Analogy: Movie studio publishes a movie under Creative Commons. They can still use it however they want.