Curry says that a big part of his decision came from his daughter Riley. The story goes that he gave her three different shoes to pick from, one from Nike, Adidas, and Under Armour.
She picked up one shoe, threw it over her shoulder, and picked up another. She grabbed the second shoe and threw it over her shoulder again. The last shoe left was an Under Armour shoe, which she brought to Steph and that’s when he said it clicked with him.
Another reason is more plausible..