One thing is the notably high level of landing fees at LCY for their general and connecting fare levels, as opposed to business pax. The E190 used there is of course significantly smaller than the A320 at Heathrow.
Quite apart from any long-haul connections, my experience on AZ from London is they carry a lot of connecting traffic to other Italian destinations through LIN and FCO - Sardinia, Sicily, Brindisi, and other points. There may be services to these points by the LoCos, but AZ can offer multiple departures per day on such connections.