This is a misconception about Asana that I encountered during a workshop recently.
In comments, you have the ability to mention (with @…) members, tasks, projects and even teams.
Even though mentioning a member will add them as a collaborator on the task and notify them, the same does not apply to other tasks, projects and teams.
You can’t notify project members or team members unless you go into the “Message” board of that project or team.
I hope this helps!