The primary motivator for doing something is always one's own benefit. Keep in mind that motives are subjective, rather than objective, and that this is more broad of a claim than it sounds. Even the idea of helping another 'selflessly' is, at the core, motivated by some kind of personal desire--even the desire for the knowledge/sentiment of having selflessly helped someone, or promoting an environment where your benefits are likely to be encouraged/preserved (such as having thievery and murder illegal). Doing something for your own benefit isn't bad, after all. It's when you start harming the personal benefits of others that it is seen as bad by those people.
I do think that one's own benefit is the primary motivator for doing something. If somebody isn't going to benefit emotionally, financially, etc, from doing something, what is the point? Even when we do something for other people, it helps us to feel good about ourselves. And that is why it is always about our own benefit.
People very rarely do something without thinking of themselves and their own personal benefit. Even when doing charitable acts it is often due to the good feeling the person gets after performing it or how other people view them for having done something good. Just about everything is done for personal gain of some kind.
I believe ones own benefit is generally the primary motivator for doing something. Humans are greedy and we generally opt to do things that serve our own interests. This has been true of humanity for a long time and it is even more true when people are subjected to capitalist economies.
Yes, one's own benefit is the primary motivator for doing something, because ultimately, humans are selfish people that mostly look out for the things that they want. Even helping someone else might look like helping, but it's often only because the person wants to feel good for doing it and saying they did.
It has been said if somebody isn't going to benefit emotionally, financially, physically from doing something, what is the point? When we do something for other people, it helps others to feel good about themselves. It makes them feel worthy of something. It is even better when you have a group that is about people helping people. Not just giving a hand out but a hand up. This is why it is not always about one's own benefit.