Simply put it is a fact that people have got used to the idea of local airport to local airport travel using aircraft almost as a glorified bus service and this to some extent is where Ryanair excel.
The snag is that like many UK bus companies, Arriva, First, and Stagecoach for example, having established a local client base they are at liberty to ascibe their own conditions and fares. Seasonal variations in fares are a prime example, as soon as the kids are on school holidays fares virtually double overnight. The airlines would answer this by saying that it helps to offset the losses through the periods when the kids are at school, which is of course total BS because as soon as the client base starts to drift away, the operators simply upsticks and go elsewhwere to cultivate another client base.
Ryanair have this down to a fine art; they cite almost any reason for moving out of an established location, air bridges, airport passenger taxes anything... Alicante is a case in point...Last year they cut something like 50% of their services, but when one takes a closer look at the actual destinations that were withdrawn they were the much smaller and less popular destinations which are no doubt being subsidised by the vastly more popular UK, German and French destinations...
Good for business up to a point because there will always be those who demand local to local and the likes of Ryan are only too happy to oblige... at a price... and provided the local authorities are prepared to offer considerable subsidiies.