Why did the Force choose Anakin to bring balance?
I don't think he was chosen because he was strong with the Force. I think he was strong with the Force because he was chosen.
But why was he chosen? How could he bring balance to the Force?
The answer I believe is: Compassion
Compassion is the only thing that can really bring balance to the Force.
This is the Star Wars version of yin and yang. The gray is the light side and the black is the dark side. But the dark side also has a bit of the light side in it and the light side has a bit of the dark side in it.
Holding them together is the circle in the center, which is compassion.
The Jedi and the Sith are completely opposite. But they have one thing in common: they both see compassion as a weakness. Compassion is central to a Jedi's life, yet they are forbidden to love or have attachments. They put limits on their compassion.
The Sith Don't encourage compassion either, they pretty much care only about themselves. That is why they fail.
"Compassion, which I would define as unconditional love is central to a Jedi's life." - Anakin Skywalker, the attack of the clones.
That takes courage. It takes great courage to truly have compassion for another person.
"Rey can still see the best in Ben Solo and be strong enough to face the worst of Kylo Ren. Compassion is never a weakness, it's courageous."
-Daisy Ridley
It takes courage to have true compassion.
Compassion is the only thing that can bring balance to the Force, yet it is not really encouraged by either side of the Force. It's no wonder that there is balance in the Force.
Anakin was really the first Force user to understand this and I think that is why the Force chose him.
Darth Sidious used Anakin's compassion to turn him to the Dark Side. It was his compassion for Padmè that led to him turning to the Dark Side.
But it was also his compassion for his son that led to him defeating Darth Sidious, and bringing balance to the Force for a time.