People actually want KOF characters in DOA...? ... Why? Don't get me wrong, I grew up off of the series and had plenty of tournament experiences but... in... DOA?! For what exactly?
Free Step Dodge
GreatDarkHero
DestructionBomb
Tell me about it. (Argentus as well, I could be wrong. It was someone in the forums.) It's like, it differs from popularity for a character and how that character works. Kyo Kusanagi is popular..but his trait and battle style disorients the game mechanics from an idea, whereas you have characters who are realistically in a combat style but not exactly popular per say.
DestructionBomb
Not to mention that TN has to take the time to provide them a 3D environment and movelist concept (Tracking, what moves will work..what won't fit. etc.)
Zeo
Angel could be in DOA, Vanessa as well, Kensou and Chris could be ported over with some heavy changes. But none of the mainstream characters like K', Kyo, Iori or the like would fit.