Why can I not turn off the loud sound for Critical alerts?

The Alertable app is designed such that it will broadcast all critical level alerts issued from authorities. Although advisory level alerts can be turned off, critical alerts cannot. However, Alertable respects your device volume and do-not-disturb settings for all alerts, even critical ones, if you have “Override Silent Mode” turned off in your Alertable settings. So, if your device volume is turned off, or you have it set to do-not-disturb (including auto do-not-disturb settings), the device will not sound when a critical-level alert arrives (although the alert notification will appear and the alert will be in the app).