Contrary to popular belief, it is almost always possible to express the 'why' (not just the 'what') via code, even if comments and/or external documentation are sometimes cleaner, simpler alternatives.

Turn around and ask. For small teams it might work well. Larger teams require more overhead, hence why hiring more people does not produce linear productivity growth.

You ask someone in slack. If that isn't sufficient, set up a small 1 on 1 meeting to discuss.

You can't avoid all meetings, but you can keep them few and small.

I have had good experiences using commit messages for documenting the reasoning behind code changes.