Cross-compiling is a need that almost no user ever has.

The only legit need on macOS was for a long time iOS only and now, the two supported CPU architectures. But that is covered by using XCode.

There would be now need for a Apple Homebrew to use or provide universal binaries.

Homebrew's design is for providing tools for the need of the single user of the system (it doesn't even work well in a multi-user environment) with the tools he needs on this system. Switching CPU architecture would be solved with reinstalling Homebrew on the new system (like it is now).