why is forms not available for numbers on MacOS
I see that forms are not available for numbers on MacOS but its available for iOS. That's a bit frustrating!
Mac mini 2018 or later
Why? is not a question that can be given a definitive answer by anyone not on one of the product development teams. That said, I suspect the reason could have to do with Forms being introduced on the app intended for smaller screens than were available on the original Mac platform.
If you think this feature would be a highly useful one on the macOS version, use the Provide Numbers Feedback menu item in the Numbers menu to send a Feature Enhancement request directly to Apple.
Regards,
Barry