Why Tons Of Noise Is Generated Between Frame Blending?

Hello guys.
I hope that I am posting in the right room.




Question.

Why is common to find high amount of noise in animated films in scenes with a lot of camera movements. Some graphics and shapes generate a lot of noise in between the blend of the frames. It is an issue related to render, layers, textures, compression, etc? I am very curious about it.

I attach two images with examples. View the images in 100% size to see the noise more in detail.




I appreciate your time to reply.




Regards!