Over 2 decades of software and hardware understand JPEG, its decoding/encoding complexity is low, and it's been around long enough that any patents on the original standard have expired. The same can't be said of the newer formats, so if you want to distribute images widely then you must use a highly compatible format. This is why I believe the other formats will always have only niche use --- remember JPEG2000? It's still around in things like PDFs and is popular for geographical applications (where the scalability and tiling features find practical use), but the immense complexity and somewhat unclear patent situation meant it never gained any widespread acceptance.