This also shows why it makes no sense for people to follow influencers and copy their trades. If some random person is publicly broadcasting their trades, they're probably (1) charging you money directly or (2) making money by influencing people's trading behavior.
No market-beating strategy has unlimited capacity, so if you truly had an amazing strategy, you should keep it to yourself. Showing it to as many people as possible is exactly how to undermine its effectiveness.
On the other hand, buying total market index funds has practically unlimited capacity, so those who own them can tell others to join the party without any effect on their own returns.