I enjoy doing robotics, but someone told me that no one cares about it. Is this true? Thanks.
Doing what you love doing is excellent for college. Trying to do things you think colleges want you to do is not so good.
If robotics is your things, then jump in deep.
Wow, I think that is completely untrue. Are you involved in FIRST? I think it is one of the most helpful ECs around. You can learn design, build, programming, project management, fundraising, marketing, and teaching skills. There are opportunities for do-ers and leaders, and it is FUN. (Pit Admin volunteer here and former team mentor, can you tell that I love it? 
) That is sour grapes on the other person’s part. If you like it, ignore them.
Doing something for 4 years is good for college. That something should be an area you are interested in. Robotics is a fine EC! You are learning about robotics, teamwork, problem solving…all great things!
One of my friend’s son was into Robotics in HS…joined an underwater robotics team at an Ivy league school…and now is working for the company that makes robotics for Amazon.
To be honest, unless it is something a bit dumb like a fan club (Star Wars Club, Anime Club, etc.), all ECs are a boost to your application. As it seems you are interested in engineering, I would recommend doing other science and math clubs, such as Math Team and Science Olympiad (Those can really help your applications!)
Sure, there are other activities that can help. But honestly, for an engineer, FIRST is a perfect activity.
@intparent
I perfectly agree, especially when they are pretty closely related. If I was planning to do engineering in college, I would definitely join robotics. If you happen to be a person who wants to major in science, then do a science club and math club, as the subjects are closely related (Specifically chemistry and physics).
Sure, if your school has them and you like them. My Physics major (now PhD student) had Robotics & US Biology Olympiad as her main “STEM” activities in HS, along with some non-STEM stuff. Her team accomplished a lot more in Robotics that she did in the Olympiad, and she still got in everyplace she applied, including some top schools.