Perhaps a route to Strasbourg with Volotea might be something to pursue for summer 2022 ? Alternatively, would Binter Canarias consider a route with an E195 to Tenerife North airport ?
If there are no capacity issues, why would these airlines choose SEN over an airport with more 'brand recognition' i.e. a 'proper' London airport.
Is SEN the short-haul equivalent of the Gatwick long haul 'waiting room'? Where you have to go where you can't get where you really want to go?