Why would they? If you've been following SNK even just a little, they have completely moved away from 2D graphics. The last 2D KoF was expensive and time consuming and they said "nope, not doing that again"
Because why not? Todays trend are nostalgia, classic and retro style games . Games Like the New Megaman are great and many 2d platformer games selling good on the market especially from indies titles like Shantae.
Just make the games mechanic original but with improvement and upgrade the graphic using 3d background with artistic style, will sell the games like crazy. I see the same pattern with 2d fighting games like Street Fighter, Guilty Gear Xrd and Samurai Shodown. Also 3d polygon actually cheaper rather than creating 2d sprite on HD system. Guilty Gear Xrd, Street Fighter and Samurai Shodown are using Unreal 4. It's faster, cheaper and can be used on many platform.