Why Study Economics - It's Fun!

Because I enjoy the topic. That's an absolute must to study economics. I wouldn't suggest anyone study economics if they do not enjoy at least some of the topics involved. Like anything in life, you get out of studying economics what you put in. Don't study economics because you think it's the route to a high paying job - you'll likely hate the program so much that you drop out (or fail) and if you do end up graduating, you might find you don't like the jobs your degree has made you qualified for.
That being said, I don't think it's a requirement that you love every aspect of the discipline. I quite enjoy microeconomics, industrial organization, and game theory. Econometrics? Not so much. As an undergraduate there were enough topics I liked that it helped me get through the ones I found difficult or did not really care for.
Terrific Job Opportunities for Economics Graduates
Because there are many opportunities for economics graduates. You are not guaranteed a good-paying job with an economics degree, but your chances are higher than in other programs. One of my interests as an undergraduate was philosophy, but I decided not to major in that because it seemed that the only possibility after completing my degree was law school - which did not appeal to me. With an economics degree you can work in a variety of different fields from finance and banking, public policy, sales and marketing, civil service (government departments, the Federal Reserve, etc.), insurance and actuarial work, etc. You can also go on to do further studies in economics, political science, business, or a variety of other fields. If you're certain your interest is in the business world, a business degree may be a better fit, but an economics degree does open a lot of doors.
Economics Knowledge Is Useful At a Personal Level
Because you learn a lot of skills and knowledge that you can apply to other jobs or to your personal life. Learning about interest rates, exchange rates, economic indicators and equity markets can help you make better decisions about investing and obtaining mortgages. The statistical skills I gained I've used again and again, mostly in business settings. I also learned a fair bit about Microsoft Excel in my first two years in economics, which has aided me greatly.
Economists Understand Unintended Consequences
Because economics teaches students how to understand and spot secondary effects and possible unintended consequences. This may seem relatively unimportant, but it's the most useful thing I've received from my economics training. Most economics problems have secondary effects - the deadweight loss from taxation is one such secondary effect. A government creates a tax to pay for some needed social program, but the secondary effect of that tax is that it changes people's behavior, causing economic growth to slow. By learning more about economics and working on hundreds of economics problems, you learn the skill of being able to spot secondary effects and unintended consequences in other areas. This can help you make better decisions about your personal life and make you more valuable to business; "what are the possible secondary effects from the proposed marketing campaign?" It likely won't help you get a job, but being able to spot and understand the importance of secondary effects, it may help you keep a job or earn a promotion that much faster. Economics Provides an Understanding of How The World Works
Because you will learn more about how the world works. You will learn more about the impact decisions have on the firm, industry, and national level. You will learn more about the impact of international trade, both good and bad. You will discover the effect government policies have on the economy and on employment; again both good and bad. It will help you make more informed decisions as both a consumer and as a voter. Furthermore, I personally believe that having a more economically literate set of bureaucrats, politicians, and journalists would be great for society - so long as they always keep an open mind about what they've been exposed to. Economics, when done properly, shouldn't so much tell people what to think, rather it should give them tools about how to think of things more clearly and realizing the assumptions they may be making.
These are my reasons for studying economics. What are yours? I'd love to hear about them.