do they list the airlines somewhere? they dont seem to be listing ryanair for example.
More seriously, I would expect RyanAir charges a hefty fee to third parties who want access to their API, just like they change much higher fees to passengers who use a credit card than other airlines.
EDIT: Atually RyanAir is there (London -> Knock)
for example: LBC is only listed with two possible destinations but there are at least 6.