The best reason in my opinion is not what most people would say. Either to help people or to make money. I would state it in such a way as to explain why it's valuable to study psychology at all, regardless of what you plan to do with it. The idea is that, as I often say, we are social animals. Secondly, the trend in society is for projects to get bigger and more complicated and more ambitious. Therefore, you will have the greatest impact on society and on your own life as a member of a team of some sort. Understanding social dynamics and how people think is a very valuable talent to have. Studying psychology will help you do that. Of course, my own opinion is that psychology is fascinating. But others may not agree, at least at first. But human psychology is a tool that will help you maximize your impact and multiply your success. I've read and studied psychology, both at university and from "pop" psychology texts, and while I find them necessarily repetitive -- I mean, whenever something is correct, others have a high probability of agreeing and repeating the ideas, right -- they generally tend to be useful and enlightening.
With a degree in pych you can basically be a clinical therapist, social worker and so much more. However people who chose this field dont quite get paid as much. People who chose this career are more about the positive change they make rather then making money. It is a service job whatever it is a social worker for children , foster or Adult protective service for elders or general clinical therapist. If you're heart is not in it and you dont have a passion then it is not a field for you. The benefits are when you see a former patient succeed and overcomes an obstacle or a certain situation and at the end you are the reason why they have been able to achieve that obstacle in that part of their lives. You get to attain akwlodge and insight of behavioral and why we humans act in certain situation difffernlty, it teaches and opens new forms of perspective that we thought was not possible. you get to be enlightened and actually get to see emotions, behavior and get to change people lives. with psych majior you can do alot more and yes it does not pay well however you still get basic benfits such as 401K plan, Pension , Sick pay ect just like a contract like others but learning this majior and getting a high degree will deffeinntly effect you as well, at times it can be heart breaking to hear certain stories and may even make you shed a tear, but always remember the patient has come to you for guidance and help and you have all the power to help them, remember there is a border line between sympathetic and empathy.
Traditionally, psychologists belonged to the helping profession, and students may be motivated to study psychology to understand themselves and others better--in order to help others with their problems. Nowadays, psychology is applied to a lot of fields (e.g. marketing, AI) but better understanding of human behavior is still a common reason.