Facebook notification bar on mobile vs web [on hold]

If you observe, you can "Mark as read" in the notification bar in the web application. However, the same is missing in the native app.

I am trying to understand the reasons/logic behind it.

Also, Facebook did have the "Mark as read" option earlier in the native apps. Based on the communication on this link: https://www.facebook.com/help/community/question/?id=10152551552787230

My question is:

  1. Is it due to real estate available over mobile?
  2. Does user not expect to mark all notification as read after refreshing the notifications? (based on above link)
  3. Does it affect user experience adversely?