Yeah, that's unusual. I mean, gaming is their target audience, and nearly all PC gamers have a Windows PC, but still. I'm sure plenty of people who use Mac or Linux at work would love an NES-themed keyboard.
I have an 8bitdo controller and arcade stick, and they're fantastic. If this keyboard used QMK, it would be a must-have for me.
That probably has to do with the software. It's a wireless keyboard, so it doesn't support VIA and uses its own proprietary software instead, which probably won't work in Linux or MacOS.
Nothing leading up to this point could have clued me in to the fact that I exist in the timeline where a retro controller manufacturer also makes a mechanical keyboard