Why do I have to take Spanish to fulfill core requirements?

I'm going to rephrase your question into two sub-questions and then answer both of them:

Question 1: Why does my college have a foreign language requirement?

Someone in a position of power in your college thought it would be a good idea for everyone who graduates from the school to speak two languages. It's not a terrible idea: Speaking multiple languages allows you to pursue a wider variety of jobs, and allows you to travel and be more worldly. They advocated for that, and convinced their colleagues to agree. If you want to change it, you're welcome to try, but honestly it's probably easier to learn spanish than it is to get your school to drop their foreign language requirement.

Question 2: Why should I comply with the foreign language requirement at my college?

Because you want a college degree.

(Bonus) Question #3: What should I do when I have to do things I don't want to do?

You're not going to like the answer to this question, but it's what I think you need to hear. If you've already decided that you're going to do it (see question #2), then you might as well get do it RIGHT. Here's why: once I started my first job and started working with other people, I came to realize that people who can suffer through things they don't like doing and still do them well are at a HUGE advantage in the real world. They do better at their jobs. They get promotions faster. They get better results in their relationships. And they are MUCH much happier. They're happier because instead of spending hours and days and weeks and months frustrated about having to do the things they don't want to do, they tackle them head-on, get them over with, and move on to other stuff that they enjoy. I was not one of these people. I was lazy. VERY lazy. I was lazy in high school. I was lazy in college. I didn't even realize it. Now that I've met people who don't think twice about doing things they hate doing... I've realized that I had the wrong idea all along. Your challenge isn't Spanish class. Your challenge is YOURSELF. Overcome it. I dare you to get straight As in Spanish this year.

(SUPER bonus) Question #4: How can I make my Spanish classes easier?

Wouldn't your Spanish classes be easier if you already spoke Spanish? Damn straight. So I'm not even kidding here: just learn Spanish outside of class. That should make your classes super easy. Plus, you'll speak Spanish, which is awesome. They got apps now you can use that will teach you Spanish for FREE (Duolingo for example). So go learn Spanish for real, the way you want to learn it, and your classes won't be a problem anymore. I double dare you to learn spanish.

It's hard. But you are strong. I believe in you.

Know languages, will travel! There are so many amazing things you can do and enjoy if you know another language. If you love movies, books, or just food, Spanish will open the doors to a lot of interesting experiences. And you'll be able to communicate to many people in the US in their native language. This can be a great opportunity for you.