What do you mean they ignored Emerald? The put in the Episode Delta part in ORAS. They aren't going to make a third version.
Unlike HeartGold and SoulSilver (which added all of the improvements Crystal brought to the table), Omega Ruby and Alpha Sapphire all but ignored the tweaks Emerald made to Gen III. Considering Emerald was a vast step up over the original Ruby & Sapphire, it was really disappointing imo. Platinum is even more of an improvement to Gen IV than Emerald was to Gen III, so it would be downright criminal to ignore it again.