Grayscale is easier to composite than color so if the lighting is off in one layer it isn't as noticeable or can easily be compensated for. Shots can be matched

Grayscale is easier to composite than color so if the lighting is off in one layer it isn't as noticeable or can easily be compensated for. Shots can be matched up with a common tone. I had also wondered if streaming was driving some of these changes, by reducing noise and providing better compression reducing the image to simple gradients.