It didn’t work for same reason with Overwatch - people either focused dangerous player and they died fast(and I died next, since Kritzkrieg offers no protection) or were hiding behind sentry guns, which are immune to critical hits.
There never were “right place and time”, as enemy Medic would activate their ubercharge, which protects their teammates from damage entirely, and kill us. Or, which is most humiliating way to fail, enemy Pyro reflects kritz rocket back at us.