Please tell me, could you please tell me all the reasons what has to be wrong with your teeth to get braces?

Occlusion: Ultimately, a good occlusion (how your teeth function together) will determine the longevity of your teeth (beside oral hygiene). Sometimes tooth positions in the arch is inoptimal for good occlusion, braces will help to establish this. Other main reasons are arch expansion, increase airway, treated bad oral habits (tongue thrust, mouth breather), and cosmetic concerns (crowding, gaps).