I would like to correct you there.
The Canary Islands are all year round destinations and are more popular in the summer months than in the winter. The reason the LCCs operate to the Canaries during the winter is that it is a very popular area and they can certainly make alot more money on these routes than they do on PMI etc. (especially LS! Charge over £300 [highest fares] on some BLK-TFS rotations, the mad thing is that these sell!)
I do agree with you though, the Canaries are certainly winter destinations for the LCC carriers, not so much for the charters who find themsleves filling planes during the winter and summer and this can be seen by the holiday prices during the summer! We went to Cayo Coco is Cuba for 14 nights this year with FCA Premium class because it was cheaper than a 14 night trip to Gran Canaria!