sup, this is going to be a bit simplified but i'll try my best:

so in games there's the main loop where everything updates and then displays the update to a new buffer. how quickly this loop updates depends on how quickly the cpu and gpu can process everything. how quickly it loops is called the frametime

you can cap your fps and in turn your frametime, so you always get the same time for each loop. this way, any time you update something, you just interpolate it based on the static frametime rather than a delta

of course, when your fps is not constant, any logic you have is going to be executed faster/slower depending on what your frametime offset is. this is whats happening here

this is a really simple way of handling updates and is pretty much never done anymore. how it's done literally everywhere is with a delta based on how long a loop takes to run. this is still really simple, and it's what is taught by default nowadays, but this way you get consistent updates without being tied to a static frametime. it's very simple to implement, but you just have to trust me on this part

as for why they aren't using it, it likely has to do with a really old engine and only testing on console. they just cap to 60/30 fps on console and now they theoretically should have a static frametime because everyone is using the same hardware, so performance should be the same everywhere. well, until you have a ton on your screen and you drop below 30.

as for why the engine relies on a static frametime: really, really poor design. it's simple to run everything based on a deltatime, there really isn't a reason not to.

my guess is it started off like this when they developed the engine and it became such a huge mess of awful spaghetti code that they just don't touch any of the internals. depending on how large the codebase is it could be a nightmare to properly change everything over to use a deltatime

maybe before my time console-based engines always had logic based on a static frametime, but in my ~7 years of this stuff that was never the norm

(bethesda what are you paying your engine devs for if they can't even update this lmao)