Airlines, not just Ryanair, don't like screen scraping websites for the very simple reason that it gives consumers a choice by presenting all the available routes and fares in one package.
Once they have you searching on their website you are more likely to buy a ticket, even if your first choice of dates aren't available, or your first choice of destination isn't available.
For example, if you fancy a trip to the Xmas markets in Germany but aren't fussed where, you might look at STN - SXF but if the price is too high or the timings don't suit you are probably more inclined to do a quick check on NRN and HHN than to load up the easy or bmibaby sites and start all over.
All about stickiness