The title of this post makes me feel a bit ancient but I will respond anyway. I have been working in the business for more years than I care to admit, and I get asked this question a lot.
The answer has always been simple in my mind. But let us go at it from another angle, shall we? Consider this for a moment. You are in a business that is rife with rejection, disappointment, long hours, endless rehearsals and lessons (assuming you are taking your craft seriously) and, will perhaps (if you are lucky) get you a few weeks of work here or there. You will most definitely have to find other ways to make a living so you can pay rent, pay for lessons, pay utilities and other expenses. You are living in an area that is one of the most expensive in the U.S., so paying those bills is no small feat.
Have I depressed you? That is not my intention. My point is simply to remind you how difficult it is to be in this business, and what a small percentage of Equity members actually make a living at acting.
So, WHY does anyone stick with it? Simply put: we have no choice. If you love this craft and it is your passion, you stay in the business because you must. If you can imagine doing something else, if you have questions about staying in the business, then this business is not for you.
So, when I am asked why one might remain, my answer is simple. We stay because we MUST stay. We stay because we have no choice. It is our life and we love it enough to stay even when it breaks our hearts. Don't become an actor for money, fun or fame. Be an actor because that is what you are and you cannot imagine being anything else. I hope that helps.
"Always smile at your enemies. It will keep them on their toes"