I think of homebrew as a curation service; it lets me name a piece of software and install it without having to any special diligence on it. In that use case, I _want_ them to enforce code-signing requirements; that reduces the risk that some software-supply-chain compromise will spread to my computer.

I do want the ability to install unsigned software, either because I wrote/compiled it myself locally and can't be arsed with signing, or because I'm getting it from a non-public source that doesn't want to share a copy with Apple, or because it's from a developer I trust who can't be arsed. But I never want to get unsigned software _from a curation service_.