I mention "GNU compatibility" for Bun Shell specifically because there are some incredibly commonly used GNU extensions even in the JS ecosystem like mkdir -p, and yes, even the GNU specific find extensions. I don't think we need total compatibility for everything. However, OTOH, Nushell is targeting being the default system shell, not just something off to the side. They could decide to be not GNU compatible and it's not like I'd complain, but I agree with their choice to be GNU compatible 100%, and it makes me more likely to consider it on my own machines.
I don't feel as though anyone is forcing me to do anything though, that's definitely not the tone I intended to convey.