It's not just Quora, I think about half of notifications, whether by email or on mobile, don't take you to the thing you're being notified of.

Or they insist on sending redundant notifications. Or there's a mysterious number and no way to see that actual notifications. Or the notifications won't go away. Or the notifications go away instantly. Or, naturally, the notifications are abused for spam.

As to why... I think it's one of those features that tends to get neglected, and because users are way too forgiving of broken software.