Hazel eyes are not the MOST common, but they're definitely not rare either.
For some reason, hazel eyes are most common in people of these regions or with this type of ancestry. One theory is that the groups listed are very mixed-- they have European, African, and Asian roots and so ''in-between'' colors like hazel are common because these people carry so many mixed genes, including those for blue, green, brown, etc. eyes whereas people of "pure" ancestry have a more limited gene pool and are just likely to inherit either brown or blue eyes depending on where they are from.
All eye colors are recessive to brown.
Hazel and any medium/mixed colors usually have the most patterns, or at least, the most visible patterns. With blue and brown eyes, they are just one solid color, so even if there are multiple layers of brown or blue, you won't be able to see patterns. Hazel, on the other hand, are green, brown, gold, orange, etc. so because each layer is different, you can usually see what each layer is doing (forming a starburst, stripes, spots, flecks, etc.).
(Think of it like this: if you color on a blue canvas with just blue paint, you won't really be able to see much in terms of patterns. Yet, if you have a grey canvas and you use brown, green, yellow/gold and orange paint, the patterns you make will be easy to see.)
Most "white" Americans are mixed- They have Southern, Western, Northern European ancestry, maybe some African blood, and maybe some Native American blood, etc. So brown eyes are more common than blue. In most of Europe, however, blue eyes are the most common.