Centre Cities
It is again a known fact that Ryanair will approach an airport and open a new route for which if I recall they can guarantee 115,000 pax per route per annum. In return for this they will say to the airport how much are you going to pay us per passenger for giving you 115,000 pax per annum per route extra through your terminals. Some airports pass and others are prepared to pay. In which case if you pay its normally a per head fee back to Ryanair, hence FRīs success in secondary located airfields. Now the airport have to look to the extra pax for income in terms of spend and parking etc...
I guess and only guess that BHX are not open to this deal hence no FR, but this case would say to me that more pax does not mean more landing fees or more taxes as in this case the airport have to pay FR and not receive enough taxes / landing fees from them to make it viable to have the carrier. In BHX case they will hold out for other carriers to serve routes through natural growth if they are happy with the airports current performance.
Only my humble opionion and may be wrong!!!!!