I am not saying that everyone is selfish and every action is selfish; I am trying to highlight that every decision is in part for yourself, which a lot of people don't seem to realize. Whenever you do something for someone else, it is also partially for yourself - you get something out of it.
If you want someone to be happy or want them to do well, it is literally want you want. Maybe they don't want that or care for that. Additionally, what you really want is probably to think that they are happy or that they are doing well, regardless how they feel about it themselves. For example, grandmothers usually want to feed you and want you to feel full. However, even when you feel full, they still want you to eat if they don't think you feel full. It is more about how they feel/think about your situation than how you feel/think about it. Similarly, your parents might want the best for you. However, often times, what they really want is for you to have what they think is the best for you.
In general, when you are doing something for others, it could also be partially because it makes you feel like a "good" person/friend/parent/child/husband/boyfriend/whatever else, it makes you feel like you are staying true to yourself/you are living up to your image of yourself, it makes you feel happy, it makes people more likely to perceive you in a way that you want people to, or it makes you feel some type of way that you like/benefit from. Yes, things can be done out of kindness or love and things can be done for someone else, but you also get something out of it. It is an important perspective to understand and could provide relevant insights in your decision-making process.
As a sidenote, I suppose you could do something completely randomly and mindlessly, ultimately not providing you with anything. However, at that point, is that really for someone else? Also, that is completely against how I make decisions and live my life. Intentionality is where it's at.