Why have the rules stopped working?

Some weeks ago, all the rules I've created to help me manage Outlook, emails I get, etc., have stopped working in Outlook at work. Every morning when I log into Windows, then open Outlook, it just sits there. I've got hundreds of emails each morning, most of which aren't things I need to look at immediately, which is why I've spent a long-time writing rules. I've gotten into the habit of going to Rules in the ribbon, Manage Rules and Alerts, then manually clicking the "Run Rules Now" button there.

Every morning. 

Why is this now necessary?