https://www.atsb.gov.au/publications.../aair200004070
Here's a good example of an accident that was partly caused when a station on CTAF witnessed two aircraft in close proximity and told the aircraft (non directed) to 'go-round'. The lower, leading aircraft complied and climbed into the upper aircraft which had not responded. Luckily both pilots survived, because Grobs are built like tanks.
Without directed information to de-conflict the situation ie, tell the upper aircraft to go-round first, then you can make a situation worse than if they had just landed and hit each other on the runway. And random extra voices on the radio can get in the way of critical communication, which is why I'm not a fan at all of having extra radios on the ground putting in their two cents. Remembering that and hand helds have very limited range and you could be over-transmitting others approaching the aerodrome without knowing.