Blending frames only works in very few scenarios. It’s not something that scales well to the multitude of things that need to be shot. For example, If something enters the frame, how do you blend backwards without a frame to do so?

Frame interpolation and generation ignores the contents of the screen and softens all elements, resulting in the overly mushy results you see on TVs with motion smoothing turned on. Impacts are softer, lip syncs may be off.

To your other question, even with your stills camera, you compensate for your higher shutter speed by changing exposure elsewhere.

Either you need a wider aperture, but now you’ve set limits on your depth of field, and potential sharpness. This is part of storytelling, for both stills and motion.

Or you’ve added more noise by bumping sensitivity. Which people don’t notice as much on a still, but do with subsequent frames when noise isn’t spatially and temporally stable. You’re also not driving your sensor for extended periods of time with stills where that heat buildup of extra sensitivity can matter.

Or you need more light.

The camera is one of the most emotional parts of a film. Yes you can do all these other things, but by doing that you place hard limits on the story the camera itself tells.