grub2-mkconfig missing parameters?

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For now, I manually added back the missing parameters in GRUB_CMDLINE_LINUX, but I shouldn't have to do that in the first place (unless my memory is wrong). How would I fix this?

No, that's normal — the kernel command line in grub2.cfg will only contain the parameters that it's told to contain, it can't magically divine what those should be. (_grub_ can't, I should say ­— determining the contents of the kernel command line is anaconda's job.)

The real question is, why _didn't_ you have a line in /etc/default/grub containing:

GRUB_CMDLINE_LINUX="resume/dev/mapper/fedora_localhost--live-swap rd.md.uuid=<uuid> rd.lvm.lv=fedora_localhost-live/root rd.md.uuid=<uuid> rd.luks.uuid=<luks-uuid> rd.lvm.lv=fedora_localhost-live/swap"

Anaconda should've written it there when it installed the system originally. Perhaps something along the way deleted it (some script mangled it during the installation/removal of the nvidia driver, perhaps?

In fact, that uninstall procedure you linked to even contains this:

Remove ‘rd.driver.blacklist=nouveau’ from end of ‘GRUB_CMDLINE_LINUX=”…”‘

 ## Example row ##
 GRUB_CMDLINE_LINUX="rd.lvm.lv=fedora/swap rd.lvm.lv=fedora/root rhgb quiet"

So, as you can see, command-line arguments like the ones you inserted were expected to already be there.

/etc/default/grub is only used when manually regenerating the grub.cfg. The grubby tool that handles kernel updates simply copies existing entries to create new ones, it doesn't use the grub2 tools at all. So, that explains why your GRUB_CMDLINE_LINUX could be missing the proper arguments, without it affecting anything until you ran grub2-mkconfig.

The last occurence of a GRUB_CMDLINE_LINUX= line will replace any earlier occurences of the same line. Thus, an empty GRUB_CMDLINE_LINUX="" at the end will make the final command line empty.