Why are Windows 10 crashes not getting reported to Microsoft?

I haven't been able to confirm this 100%, but based on recent observations I believe these crash reports are tied to the "Optional diagnostic data" option in the "Diagnostics & Feedback" settings.

Optional diagnostic data setting

A few days ago I changed this setting from "Required diagnostic data" to "Optional diagnostic data", and crashes that have occurred since then are now showing as "Report sent" in the Problem Reports Viewer.

Recent unexpected shutdowns reported