Think about it, after Vanilla, the Elves were completely ignored. They're not even an enemy of anyone in the campaigns. Plus the fact that Findan was the only character to never come back after Vanilla.
They also shafted the Elves in Heroes 6. Academy was planned to be in Heroes 6 but was scratched out due to time constraints.
So what do you think, will we ever see the Elves again or has the Nagas stolen their spotlight?
I guess they found dungeon more interesting during H6, that or they wanted to tell dungeon's story. As for H5 campaigns they were kind of a mess. In the original missions you did not even get a taste of the faction you were playing(Demonlord-led sylvan with a script that weakens your army every day? Academy campaign with no academy towns past mission 1? etc)