Just a fair play thing for me. Imagine if a ref allowed someone like Salah to take a quick free kick and score against us while we are lining up our wall, after Mane had 'won' the free kick after tripping over an overgrown blade of grass, I think I would put my foot through the telly.
Ok maybe Im being a bit childish with that scenario. Maybe I have bad memories of Henry constantly trying quick free kicks against us back in the day.
Ultimatly, its just fair play to me to wait until everyones ready.