I think the reason behind no Cynder is that Cynder would have to follow rules to be Cynder. If they make a new character, they don't have to follow any rules, it is a blank slate.
By rules I mean background, appearance, sound, personality, element(s), and possibly others that I may have overlooked.
Since when does Activision follow rules?
If they were going to follow rules, Spyro wouldn't look like a four legged, bruised, goblin dog LOL
But that's just my non serious opinion.