Why don't contextual notifications appear in the app's notification center (bell icon)?

Why don't contextual notifications appear in the app's notification center (bell icon)?

Some contextual notifications are generated on the phone and not in the app, unfortunately they cannot be added to the notification center (bell icon).
This is the case for time-based contextual notification.
For time-based notifications we recommend keeping notifications shorter so that they fit into the notification box and can be read immediately.