When the Canaries routes from SEN were started it was reported that the maximum numbers of seats for sale would be restricted to 170 to Tenerife (10 unsold) and 175 to Lanzarote. Gran Canaria is almost the same distance from SEN as TFS so the same commercial considerations would presumably apply. The passenger numbers for the route suggest the customer uptake was below expectations and that would have been the reason why the route has been dropped.
The figures above were for the 180-seat A320. It would be interesting to know how it would compare in its more recent 186 seat configuration.