While searching, I found one person asking but never found the idea being discussed.
Is there a reason an option to choose the module isn't available during the assignment creation from the assignment area?
If the assignment is created in a module with the + sign then it is put into the assignment group.
It just seems odd that the page with all the details for creating an assignment doesn't have the dropdown to place it in the module.
Please let me know if this idea exists for voting and I've simply missed it.
Layne Heiny
I've been working with Canvas since 2010, and I'm not sure I've ever seen the answer to your question, because I'm not sure there really is a definitive one. I'm pretty confident that the reason this was never developed is not malicious; product managers hear from many instructors with many different workflows when they design for development. I can see where it could streamline things for some work-flows, so I would love to see this as a feature idea if you're willing to submit it in Ideas.
You may also want to follow Priority: Assignments 2.0 and provide input there when opportunities are available.