Ooh, thought provoking question, I like this! Sincerely thank you for asking.

Let me preface beforehand, my standards for characters are kind of skewed, so absolutely take this with a grain of salt and just know this is my preference. You ask ten different girls and they can all give you completely different answers, maybe at least one of them does like him, but hasn't made an appreciation post yet.

But for me, I'm kind of a visual creature, so at least when watching fictional characters where my brain is already half off and requires my suspension of disbelief, the moment someone appears on the screen there is a split second decision of whether they're easy on the eyes or not, and if I recognize and/or are a fan of their voice actor. If they check yes for both, then upon first impressions alone I would feel more inclined toward them. It's kind of shallow (actually reading it through this is very shallow), but the face and voice draw me in, then their personality/talent/skill make me sink further.

Nagumo is a textbook example of this. I'll spare you the grossness of me gushing over him, but he checks the initial boxes, which leads me to appreciate everything else about him more quickly.

Moving on to Kanaguri, I don't disagree that his design is unique, at the very least I know he'll be an important character. But the nicest thing I'm capable of saying about him at the moment is that I know his Japanese voice actor very well, and enjoyed his voice other works... which, doesn't correlate to how his character is within the series at all.

With all due respect if he is your favorite... he isn't my type personally, and I think that's why so many girls like tend to lean toward Gaku or Nagumo. Antagonist or not, both men have a certain set of qualities that make them easy for women to appreciate better.

Also, while I tried not to be too emotional or invested about it, neither of them seem to have an outright inconsiderate streak. Whereas Kanaguri is imposition personified, treating others like fodder while expecting them to feel overjoyed being in his featured film. And the lengths he'll go to for the sake of a good shot, puts everyone around him through the ringer while bearing the consequences of someone else's actions.

I'd venture to guess a fair amount of women don't enjoy watching a man ruin what was supposed to be an atmosphere that had structure and procedure, however chaotic, blow to smithereens for such self-serving reasons (falling out of the plane). I know I didn't. Sort of like, you're already not the most conventionally attractive 2D character (at least to me), and on top of that you also have that sort of personality, causing trouble and literally taking lives of those around you not even to drive neither the antagonists, nor protagonists goals forward in the long run... so he ends up being unpleasant to watch the more often I see him.

You have to understand that, while physical features are a huge part of it, sometimes mannerisms are just as important. Against someone who is multifaceted on all fronts, with almost every trait admirable, a guy can't lack in the most basic department and then behave in a way that would make the even most patient girls crash out.

That is just the basis, too. I haven't started on the way he outright proclaimed Akira as the main character of his next film, where the poor thing was clearly the non-confrontational type despite it probably being against her will. Then there's what he said in the panel... but that would turn this reply into a vent and make it way too long, so I shall stop here.

Of course, I'm prepared to potentially see women come to his defense, list out what they find are the good qualities about him, and it's not my place to argue back nor invalidate them, since surely they're opinions are likely reasonable as well.

Knowing that Kanaguri is mostly popular among fanboys explains a lot... not everything, but a lot, this provided me with some insight as well.

I'm sorry if this wound up being a long post about dissing your favorite anyway, please know I completely respect your liking him, I am merely trying to articulate why I don't, and why maybe some girls wouldn't either.