I don't think there are "pure" reasons for doing anything. If we think we are doing something for one reason, that's just the reason we have decided to concentrate on, see, "want" for ourselves.

When we decide to help someone else, we could stop first and think about all the various reasons we are doing it or what it is possible to get out of it but usually we don't want or need to at that time; if we think too much, nothing gets done, we get tangled up in the thinking!

I hear you saying you feel bad that you get anything out of helping someone else when you want to help someone else, but why shouldn't you get some personal satisfaction from it? It's your life and you have to do things that help that life move forward, that's your job. If you are a college guy taking a summer job helping people move and love that you can take your shirt off and get a good tan and build strong muscles; there's nothing wrong there! That's all good! As long as you do the "helping people move" part to the best of your abilities; everyone gets what helps them, the other people and you, for yourself.