Why is popularity so important in high school?

Because it determines your reputation and to find yourself whether you want to be popular or not.. You just are if you are nice to everyone and you are a "cool" person dressing in the latest styles and talking like the popular people too, Besides people want to fit into the popular crowd but not everyone can so I would recommend just being yourself and no one NEEDS to be popular to feel accepted.

Because most people think that popularity means liked and accepted, which in many cases isn't true because in my high school, the people who talk of themselves as 'popular' are actually disliked by lots of normal people. And yes popularity is important to some people more than others. To me it doesent really play a role in my life, as long as I have friends and that I'm nice to people

It depends on the person.
Some cherish popularity more than others.
And for some people, being popular remains important their entire lives.

It isn't important. Oh please, high school is a phase in your life. A mere chapter in your story which is your life. Who cares if you are "accepted" by those people. You will most likely not even keep contact with most of them. The opinions that do matter are of your co-workers and boss when you finish high school and get a career in the real world. It's fine to have friends in high school, but don't be so focused on being the most well liked because in the end it doesn't matter and it's not like you will remember most of their names twenty years down the line anyways. I find it sad how some people live for being "popular" when in reality, it doesn't even matter in high school.

there's a song by bowling for soup titles "high school never ends". Its rather vulgar but truer words have never been. Though popularity isn't ever going to be all that important. The best and worst aspects of high school itself will resonate throughout the chapters of your life.

your going to get a job and find that there are still teachers pets but instead of not getting in trouble they will be getting away with improper conduct in the workplace. You will still see the little cliques that speak ill of others. Your still gonna have the super smart people. There will still be the people fighting desperately to find the next big trend. And there will still be those who cant keep up with the current ones. The question is never why it is so important now. The question is are you going to waste away your life in high school trying to become popular only to have to start over or use it as a proving ground to better yourself when the safety net of high school is removed upon graduation. 

your still young. Run around enjoy your breaks and remember who your real friends are. Because they will be the ones who pick you up when you fall. :)