When you look at 'Taxes/Fees' just above 'Total Price' in the select phase when booking on Ryanair you will notice that the taxes and fees are actually €10 cheaper at Knock Airport in comparison to Dublin airport. The €10 you pay at Knock evens the total taxes/fees you pay over all, making it the same total cost as Dublin. In the end you are not paying anymore in fee/taxes. I know charging €10 at the gate isn’t ideal but you simply aren’t paying anymore.
Besides you save on car parking costs at Knock. Parking literally 2 minutes away from the terminal when compared to the more expensive short term parking beside Dublin airport.
The airport is governed by a trust where all profits are re-invested in the Airport. I have no link to, or family employed by, the airport, but after a fair few years living in the UK see it as a god send for getting home. Wish more people would get behind the airport instead of constantly criticising a facility that is there to service the community.