The Gamer is not magic. It is not tech. It is its own thing, orthogonal to other things.
Harry potter-style wanded magic is a very specific area of endeavor, with its own built-up traditions, personae, and so forth. Getting into that pretty much requires showing up on the appropriate radars, getting sucked into the applicable storylines *very* early on, and so forth. It is defining. You are a wizard or you are not. A lot of us don't want to be a wizard.
We're Dudley. Much of our self-identity has been built around not being a freak like that. Our parents didn't really talk to us about what it meant, but the message came across loud and clear. As Dudley, especially, I could see a definite sort of pride in deciding that hey - we don't *need* wizardry. We can beat them without it.
Wizardry is easy-mode. It's the one tool that does everything - and as the Gamer, we're ridiculously good at learning things. If we go down the magic path, we'll almost inevitably wind up hugely overpowered, to the point that either we steamroll everything or newer and more threatening challenges have to be created just to have a hope of opposing us. Regardless of which it is, once we've given in to wand-wizardry and built up some competence at it, it'll almost inevitably be enough better than any other way we could solve problems that it will define our decision space except in those few cases where, for whatever reason, it's denied to us. Many of us don't want to play that game.
"Ridiculously powerful wizard" is something that the HP-world wizards can understand, accept, and deal with. "Muggle who somehow manages to flatten us all entirely without magic" isn't. It'll be a bit reality-breaking for them, and it's likely to be *hilarious*.
I have no problem with multiclassing. I like the idea of multiclassing. I just don't want "wand wizard" to be one of the classes we take.
Have some "why"s.
