Caring is a human trait but some people have allowed other emotions to bury their caring nature. It is something that is almost certainly learned, or lies dormant for the first few years of life. I think you would agree that the only person a baby really cares about is itself! Getting its own needs met is a full-time occupation, and it learns what caring is and how to do it only through observing other people, and in some cases overt teaching by a parent, teacher or religious leader.
If you keep your eyes open, there are lots of good examples in your life of people you can learn from and caring requires you to be emotionally available and open. But sometimes we don't feel like being open. It's easier to keep things to ourselves. That's OK sometimes, but every time you say "I don't care" about anything or anyone, you distance yourself from the issue and from other people who do care about the issue and close off opportunities.
It can also look like laziness when you don't even offer an opinion. It is rather lazy and kind of mean to ignore things that are important to people who are important to you. Imagine if you opened up about a topic that was close to your heart, and others couldn't be bothered to pay attention or comment. Maybe that has happened to you already.
I'm not saying that you have to care about every single thing, but caring enough to give this issue a little thought, and caring enough to let people know what you think, can create the open channel of communication, which is key to building relationships.
Even if people don't agree with you (and it's okay and even desirable to have differing opinions from others), by taking the time to decide how you feel, and voicing your thoughts, you show respect for the person who initiated the conversation.
The Law of Attraction states that what you focus on expands and you begin to attract more of it into your life. Therefore, focusing on caring and making it a key part of who you are will help that part of you to grow.
What do I mean by learning to care? Well I mean you can care more than you would have, if you had not been focused on it. I also mean caring more than the average person does. It does take extra effort, but that effort is always rewarded. I first heard the following quotation over 25 years ago, and it still rings true for me and guides my work:
"There are no traffic jams on the extra mile." Zig Ziglar
Fantastic concept isn't it? Since so many people are unwilling to put in that extra effort, to go that extra mile, the people who do really stand out. When do you have an opportunity to go the extra mile and care more than you normally do, or more than the person next to you?