EVGA is Nvidia and Intel only. Why? From what I understand it has to do with EVGA's relationship with Nvidia. EVGA gets to market special products by being Nvidia only, such as the KingPin editions and what not.
Even if that wasn't the case... most gamers today are running Intel. Why does this matter? If EVGA spends say, $500,000 on research and development of an AMD board and wants to sell them at $250 a piece. That's 2000 boards they need to sell to make their costs for development, then there is also equipment costs, labor, the power... There's a lot of hidden stuff that the consumer never considers.
At the end of the day, there is someone at EVGA with his pencil and his calculators that has already done the math. It's just simply not worth it to EVGA to make AMD boards.
EVGA tailors to enthusiasts. At the moment, AMD just doesn't cut it. Zen could be big, but i'm tired of the AMD hype personally.