I mean, boxers have coaches/corner men, UFC fighters have coaches/corners, racing sports drivers have whole teams of support.. I don't think it's more of an individual vs. team thing, I think it's just how sports in general work, with a couple of exceptions for very straightforward sports.
If people want to give each other advice, that should be fine.
How many corner men are people they'll be fighting next week? How often do they get to just extend the match because someone decided to talk longer or a crowd buddy came up and gave advice? How often do they beat their opponent and then go fight the guy who just gave them advice 10 minutes ago?
And team sports like football/racing are already a completely different beast. It's already not 1v1 and many of the same arguments still apply. You can't just have someone jump down from the crowd and start calling plays because they were an ex player and know what's going on. You have to be registerd and on the team to be involved in the play. Not just some buddy.
The vast majority of digital sports do NOT allow "non players" to participate because it's been shown to be detrimental. A major example has been team sports like dota/league/hots/csgo, where the addition of a "coach" who's allowed to watch over your shoulder can completely change what skills the game is testing. There is a limited stack of information a human can process, and it gets a lot fucking easier when you've got a coach watching your minimap over your shoulder to call out things you wouldn't have noticed otherwise.
In a 1v1 competitive game I want to know who the best player is. Not the strongest support group If you labbed the matchup, great. If you didn't, well I hope you can adapt. If you can't, you deserve to lose, not get your ass pulled out of the fire because your buddy comes over and tells you some OS you weren't aware of, or gives insight into patterns he noticed while you were getting your ass kicked. It's literally giving an advantage to the people who are already in the community.
Alternatively, if you're going to allow it, fine. Lets give 5 minutes between every match for people to look up tech on twitter and hop into training to lab it. Why stop at "who has the most friends".
Edit-
Ill also accept "you have to register your coach, they're on your team, and they cannot compete". None of this "oh shit I got eliminated in pools so i guess i'll go give advice to my buddy" bs.