Taxi Driver

Taxi Driver is a film from 1976 direct by Martin Scorsese. There are many strange elements that make this film so significant. Such as the main characters lack of direct focus and obsessive focus on specific things while also a lack of dialogue to express this. Most of the time the main character, Travis, played by Robert De Niro is simply silent to himself and observing the things around him. The few times he speaks is it with great contrast from the way he behaves towards specific people. He he no interest in conversing with fellow men however very interested in a beautiful woman. Travis repeatedly becomes very intrigued and almost obsessed with women. First with the girl from the campaign and second with a young girl prostitute.  He becomes very eager to help them in a way, however, it's strange because the audience is unsure of what he gets out of the situation.
Why do you think Travis does this?