AMD has lately latched onto being the 'bargain brand' that offers comfortable performance for affordable pricing, but that doesn't stop people from building powerful rigs with them. If you like the performance of your AMD, then stay with it. The one you have in your sig is a really stout machine.
Why are there more Intel-based boards? part of that answer is market share, Intel has about 70% of the market. Another part is Intel also makes motherboards as well, and do so for every advancement they make, every die shrink and every new architecture they produce, and every new feature that comes out.