It's a UK website. Cheerios are relatively new here, and my impression is that they aren't very popular. In particular, i suspect they haven't caught on with the demographic of people who write articles for the BHF website.
I'm not sure "relatively new" is accurate, though of course it depends on the timescale. They seemed as widespread as other common sugary cereals (Coco Pops, Frosties, Ricicles et al) during the 90s. However, if we're looking back further, it could well be the case that they were comparatively late arrivals.
