Why were the ground wires in my light boxes either cut off or tucked away unused?
You hit it with lazy.
Code requires metal fixtures to be grounded so not doing this is both lazy and a code violation.
I don’t understand why some snip unused grounds for plastic fixtures possibly lazy again because it is faster to snip than tuck it back in the box.
I always tuck them in the box if not used but I have found many that snip.