It covers the impact of fuel quite thoroughly but it brushes over the time element which I think is actually a bigger factor in why they don't really do it. Passing on the fuel cost to the customer they could probably get away with but given how tightly packed the flight schedules are (particularly short haul) the cumulative extra time across even a day could be enough that they have to drop a flight from the schedule.

When you consider that RyanAir don't have seat back pockets specifically because of the extra cleaning time to clear them between flights, you can see why the extra 2 minutes flight time might matter.