it's because I want toUsually used after a verb stem with -고 싶어서 그래요 to explain that someone is doing something because they want to do it. The subject is often omitted and understood from context. The casual form is 싶어서 그래.
KO: 왜 이걸 주셨어요? 제가 드리고 싶어서 그래요.
EN: Why did you give me this? It's because I wanted to give it to you.