Pax Vobiscum,
You're wrong in your assertion that "you won't find [Ryanair] flying to Barcelona or any other major airport". Madrid? Gatwick? Stansted? Had you written "many major airports", I would agree that this is currently the case.
I have thought in the past that perhaps Ryanair might be re-thinking its strategy, as there's a limit to the number of "secondary" airports it can profitably serve whilst generating large passenger volumes. Such a shift would show recognition of the strength of demand to fly to/from major airports situated near large urban areas.
Just one example: Ryanair inherited the Stansted-Murcia route when it took over buzz. Yet it later opened Alicante as a base.