The stadiums were "empty" because the photos were taken during practice or pre-game. It's not like they would let some Topps photographer on the field during the game back in 1957.
And, while I agree the photography isn't up to modern standards, I think the 57 set gets a bad rap for "muddy" or "dull" pics in large part because of the Mantle card, which I think they purposely "muted" in order to wash out the bat boy in the background.
However, there's plenty of full color shots like this in the set too.
