Show me one person who has been through life without having bruises, been beaten, scarred, broken, betrayed, or had horrible setbacks.
Show me a deeply competitive person who has a clean past and nothing to inspire that competition.
Show me any superhero or supervillain who does not have a tragic backstory.
Show me any person in history who has met with no resistance in their life who skated through and been noteworthy.
Show me any of those things and I will show you a person who is lying.
Nobody worth writing about is untouched. We are all products of our environment, our upbringing, our successes, and our tragedies. More importantly, we want to read interesting stories. We want to see people who have been through the shit we have been through or worse and made it through. Nobody wants to read the story of a supervillain who has no reason other than his evil nature to drive him into doing more evil.
Steins Gate MC has no tragic past and remains a fantastic character.
Rewrite MC has a past but it is not tragic. And
his best version is in the true route, in which he has no past
Takeru from Muv Luv has no tragic past and goes from annoying to a great MC.
Rin from Fate Stay Night has no tragic events and is the best developed heroine.
Main girl from Acting Lesson: again no tragic past.
Take Mass Effect best trio: Liara, Tali and Garrus. No tragic past. The three of them grow IN game.
Those are just the top of my head without thinking much.
You never saw competitive children that are competitive just because? Really? Me and my friends were competitive because it was fun.
So while everybody has suffered something, not everyone is scared terribly but it.
And you are totally missing the point and in fact you are saying something false. NOT ALL STORIES NEED TO START WITH A PAST. I put it large because you assume that is the case. You can make all kind of tragedies and conflict and drama during the story.
Not all characters are interesting because of their past. And certainly not only tragic past are interesting.
Even in a Rick and Morty episode Rick makes fan of how all superheroes are all the same. Rick and Morty!
So no, you dont necessarily need a tragic past to make great characters. If anything, is done half because you want the audience to be empathetic but also because it is an easier way to introduce mystery. You give some hints and then "what happened to him/her"
Now, I am not saying we dont need tragic past either at all. Amane' past in is The Fruit of Grusaia is the best part of the novel. And in this novel by construction all characters have a tragic past.
My favorite novel of all time, The House in Fata Morgana, is about discovering tragedies, oversimplifying stuff. But this is by construction. Not all novels NEED to be like that.
Also, it can be detrimental. If a character past is too harsh, it can make new tragedies less effective. "Why care he has no job? Girl was raped!" "Why is he so devastated heroine died? His family alwaya die. Why this one matter so much?"
Again, I am the biggest drama queen here. I love to see characters falling in despair. But no need to make everyone broken from the start. Can brake them in game. And characters can have flaws that make them interesting without a past generating them.