To be fair to Ryanair, they're pretty open about this. And when you do get the ridiculously low fares, this is why. There's a lot of money saved in avoiding re-routing customers, endorsing, giving meal vouchers, hotel accommodation... Basically, any contingency.

I'm sure they'd be quick to point out other practices that full-service carriers use that they don't, such as overbooking, cancelling subsequent legs of a flight if you miss one, etc.

I don't like flying on them, personally, I find it too much of a hassle (including getting to STN). But when you get a fare for a fifth of the closest competitor, as has happened to me in the past... Well, you get what you pay for.