I came across the news about Fallout 76 has a problem: you can edit a value in one of the ini files which affects the frame rate, and then the physics engine is tied to that, with the end result is players are able to move faster simply by rendering more frames. Obviously this is a problem but why do developers design the physics engines around a frame rate? You need to have a rate of change. Frame rate is a convenient source of what the rate is.
A lot of equations in physics are over time. Meaning they measure something that happens between two points in time. Take velocity: it's the distance between two points in space divided by the time it took for something to travel that distance. Acceleration is the rate at which an object changes its velocity between two points in time. The problem with physics simulations in games (and perhaps in general) is that everything being calculated is being calculated for an instant of time. You might be able to know the input parameters, like how fast an object was going, but you won't know if the velocity will change in the future even if you knew all of the factors that are affecting it because you need one more thing: how long is the object going to be subjected to these effects? Or to put it in another way it's like asking this: I have an object going 5 meters per second, it's experiencing a acceleration of -1 m/s^2, what's its velocity going to be? I don't know, because I don't know how long this object will be experiencing said acceleration.
What Bethesda is doing though is they likely have a reasonably frequent enough rate at which the physics simulation is run at. But they also cap the frame rate to that rate as well. This may also cap the input sampling rate. So why would they do this? Because rendering faster than the rate at which the physics are simulated would mean rendering extra frames that don't add any new information. This may have been a design choice, because other developers don't seem to care like what Ubisoft does with Assassin's Creed:
The cloth runs at "half frame rate" because the physics engine for this isn't ran as fast the graphics rendering is, and so you have this weird effect with the cloth seems to move at a disjointed rate.
So when you uncap the frame rate in a Bethesda game, you're effectively telling the game to run the physics engine at a faster rate, which is great!... except for the fact that if everything else about the game was designed around this one value and affects how everything else behaves. Really the solution to Bethesda's problem is to not make this value changeable in the first place. Or I guess, you know, design a physics engine that isn't dependent on frame rates.