GH actions templates don’t build all branches by default. I guess it’s due to them not wanting the free tier to use to much resources. But I consider it an anti-pattern to not build everything at each push.

That is because GH Actions is event based, that is more powerful and flexible than just triggering on every push and not letting it be configured.

``` on: push ```

is the event trigger to act on every push.

You'll waste a lot of CI on building everything in my opinion, I only really care about the pull request.