As I have been using tmux for a long time, I have configured oh-my-tmux on my machine. I think many users will have this pre-configured. The idea would be to have instructions in the documentation on how to install better-tmux for those who already have oh-my-zsh configured.
In this case, I managed to remove it here by removing the oh-my-tmux repo from my environment, but it may be recurring for other users.
Reference:
gpakosz/.tmux#678 (comment)