The Homebrew devs originally decided not to duplicate software bundled in macOS, and to build against what was already available. I could see advantages to this, but Apple often left us with such outdated stuff.

The original solution was to tap homebrew-dupes, then install your tool. So for example:

$ brew info bc
==> From:

Hey, wait a minute. The URL points to homebrew-core now. Has homebrew-dupes been depracated?

Homebrew/dupes (depracated)
These formulae were those that duplicated software provided by macOS. All formulae were migrated to Homebrew/homebrew-core
Latest commit by MikeMcQuaid 3 months ago.

How about that! I approve of this.