I can’t really speak to Fuchsia systems, but a lot (most?) Linux desktop distros use stub or systemd-boot bootloading these days. And if you want to get fancy, there’s rEFInd.
Which ones are you thinking of? Most 'desktop' distros I've used recently still default to Grub (Debian, Fedora, Linux Mint, Ubuntu) though I'd certainly be glad if change is on the horizon.
Course I'm a few years out of date
Also why MS' bootmgr stuff is still a flaming pile of junk.
Edit: And why MS has never given us a way to dictate where it installs its junk and/or to not install its junk!!!!!!
This means you can just partition everything from Linux and then install windows safely into where you select.
To clarify a bit too, as it seems it may not have been clear: grub was never run or installed inside a fuchsia system, I was building disk images from Linux hosts.