Bandwidth is one. Going from 30fps to 60fps doesn’t necessarily double your bandwidth (due to how video compression works), but it doesn’t help.

On the recording side, things get even worse. You want very light compression, preferably none if you can. At higher resolutions, that can stress the limits of hard drive throughput, and flash storage is still expensive.

At really high resolutions and framerates, the CPU usage of just moving data around can be a stress point. You don’t want to have a CPU fan running in the background during a shoot. You need either a passive cooling solution on a low end CPU, or a bunch of thermal mass to absorb heat for the length of the shoot and then let the fan go crazy as soon as you stop. Oh, and that heat has to stay away from the camera sensor or you get thermal noise.

Then there’s lighting. Doubling the framerate means half the light hitting the sensor per frame. So you use more light. But studio lights remain expensive because they need high CRI and (especially at higher framerate) need to be flicker-free. The power supplies for LEDs to be flicker-free tend to be less efficient or more complicated, so they’re not mass market with economies of scale. Or you can use older, hotter, and even less efficient forms of lighting. The kind that can literally cook an egg on its backside.

Alternatively, you can turn up the ISO, but now you’re introducing thermal noise again. Edit: can also use a lens with a big apature, but this is also expensive and affects the depth of field (the part of the image that’s in focus).

It’s all stuff that can be solved with some amount of money, but even the LTT or Mr Beast level channels struggle to get there.