Fedora 39 - grubby no longer persistently applying kernel args?

Ran into a confusing issue recently with kernel args.

I have two PCs running Fedora. My main PC, and a PC I manage for a family member.
On my PC which I’ve upgraded through from Fedora 35 to 39, args were still persisting through kernel upgrades.
On the second PC, I had installed Fedora 38 then upgraded it to 39 when that released. I’m pretty sure the kernel args I applied while that was on 38 persisted through kernel updates while on 38, but on 39 they weren’t.

After poking around, I found my install was missing /etc/kernel/cmdline.
I ran grub2-mkconfig -o /boot/grub2/grub.cfg, which also created that file.
It didn’t have my added args and the args were wiped from all boot entries listed with grubby.
I added the args back with grubby, then restarted to the previous kernel. Removed and installed the latest. This time it didn’t inherit my existing added args. Added the args to /etc/kernel/cmdline and repeated the re-installation, and it then had them. Did the same on the second PC and got the result I wanted.

So I guess what I’m getting at is, why isn’t grubby writing new args to /etc/kernel/cmdline if that’s where they need to go for persistence?
And I wonder why I was keeping mine through kernel updates when I didn’t even have that file.

I have seen this happen as well on a system that had been upgraded from ~F34. It is very easy to copy the necessary args from /proc/cmdline and place them into /etc/kernel/cmdline.

Why this is not managed I don’t know but apparently grubby does not look at nor manage the content of that file.

grub2-mkconfig does use the arguments from /etc/default/grub in the variable set with the GRUB_CMDLINE_LINUX= line so that is where those arguments should be initially set so they persist with all kernel upgrades. I believe it also updates the /etc/kernel/cmdline file when run.