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.

In long running projects, the people who know the answer may no longer be around.

Now my ability to find something is limited by someone else's availability, and everywhere I've seen this culture it's devolved into the same 1-2 people answering all the questions as not everyone has a built up map of who knows what.

After you are the 3rd person who contacted me for the same thing, the next one better read the fking documentation that I write.

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