Ryanair and Easyjet are taking this action for the simple reason that we all know they make money out of their ancillary services such as hotels, car hire, Insurance etc etc.
These other sites simply wish to take th Ryan Easy flight and have the passengers book ancilliary extras with them instead thereby depriving Ryan and Easy of revenue.
It's a different scenario for other products and services whcih is why they don't object too much.