Ryanair has spent many years working out ways to get people to pay a LOT more than the ticket price. The days of a genuine 50p single ticket are long gone, unless you really compromise and play the game - and that's just not worth the effort (hence Michael O'Leary finally realising it's time to stop p**sing off the passengers).
Besides those super cheap sub-£10 tickets, some people on the same plane would have been paying £100-200, and still getting the exact same service. No extras, no lounge.. nothing - just paying the higher price that covers the cheap tickets. That's the way it was designed to work. Yet, I could never understand how Ryanair could sell tickets once they got to a certain price.
Now flying mostly with BA or SAS, I can say that I remember getting offered cheap upgrades to business on multiple occasions (where you do get a little more than economy, such as the lounge and nobody sitting in the middle seat - and maybe some free food).
It would have been possible to upgrade relatively late in the day and pay less than a full price Ryanair economy ticket - and even more recently, with all the extra fees levied by Ryanair that everyone will eventually fall foul of, I bet some people actually pay more.
So really it doesn't matter if one airline ONLY has economy and another has economy/business or first. It's how much the flight generates overall - and Ryanair was doing very well from that, especially when it was initially catching people out before they wised (the passenger) wised up.
Some played the game to continue paying as little as possible, but many more just stuck their fingers up to Michael, such as myself.