On which basis do you say this? I haven't seen examples of this anywhere.
Yes people were disappointed about no campaign for Vergil, but that didn't decrease his popularity as a character itself. The opposite happened, in fact. Since DMC4SE's release, God knows how many times I've seen people asking Capcom out loud to make a Vergil solo game.
I dunno which DMC related places you frequent, but I've been on GameFAQ, Twitter, Facebook, YouTube, Steam, NeoGaf, and people seem to increasingly want a Vergil game. I don't see his popularity decreased at all, let alone decreased "considerably".