This late arrival time does not provide much in the way of opportunities for connecting traffic. Getting into LGW so late does not allow for any connectivity without a 1 night stay.
Moreover, what does this late departure do for Knock airports cost base? Needing to stay open much later every day? The airport traditionally didn't have departures so late in the evening this allowing for a shorter day. Again that was a reason why a Ryanair base wouldn't be attractive.. Ie too long a day at considerable cost... Like the Blackpool example and Jet2.