Steemit Notification ?? Why ? How ?

When I was new to steemit I keep searching for notification. When people follow , upvote and reply at my post I don't get notified about it.
I kept on searching about notification and found extension on browser and many other site which can be used for notification update. Till today I am in confusion why Steemit doesn't have its own built in notification,WHY ?
This might not be my problem only. What you steemian think about it ? and solution to this problem?
Please reply me !

Happy Steeming !