> I don’t understand why people are expecting day one support for applications like Homebrew.

Because an important segment of Apple's customers--developers--rely on Homebrew for critical functionality.

Of course it's difficult to move an entire ecosystem to a new architecture, and Apple may have made the right move here. But it's not very hard to understand why people who stand to gain so much from the new architecture, but can't use it yet because the ecosystem isn't there yet, are a little annoyed.