I had never given thought to this 'problem' before this thread. Intrigued, off I went to inspect the jumpers and cardigans in my wardrobe. I found 7 pill free cotton ones, mainly from Cotton Traders - all at least 10 or more years old. Just a couple of warm, bobbled, wool ones, only worn for gardening or painting as any bobbled garments are regularly culled.
The big surprise though was two old, very warm, polo necked, tunic length, woollen jumpers, seasonally washed weekly as staples of my everyday winter wear. On close inspection, I saw that both were covered in pills, which I had never noticed because both are mottled - one navy and white, one grey, pink and cream. I had another look at a dressy, black, lightweight, fine woollen long cardigan which has silver flecks throughout. Again, I had to look very closely to see that there was some pilling, again masked by the flecks.