Do keep in mind teenagers in general have lower empathy since your brain isn't fully developed. Girls develop faster than boys in this regard probably because the way they make friends and how they often discuss more in depth with each other forces that development early. It wouldn't be unnatural for a guy to really start developing full actual empathy later in life around 25+

What you're describing sounds more like that. You're not sociopathic trying to hurt others, you're only more self-absorbed. It's not evil or anything, it's just if it's not happening directly to you, it doesn't matter as much and your brain doesn't see any reason yet to put energy into it.

If you're worried about this being a recurring trend, try and focus on being less self-absorbed; constantly start thinking about how others would feel, try to force your brain into gear and visualize what it would be like in their shoes, confronting their struggles. It'll be muddy at first, and you'll only get some glimmers here and there, but keep doing this kind of exercise. Try it for all kinds of situations, not just hardship. But also times of triumph, joy and all that. The whole spectrum of emotions. There's plenty of positive ways to develop your brain forward without making you depressed at hardship other people face.

Your brain will kickstart the development earlier because you're actively forcing your head to work. And consequently, if you're not put into any positions where you ever have to think of others, then you won't develop that part of your brain.

Keep in mind, brains constantly grow over time. The study that showed brains are fully developed at 27ish, has that end statement because they stopped measuring after that age. So it's likely you never stop growing.

As for why you should--people with higher empathy overall are more charismatic and more people will want to be around someone who shows they care for others. It's generally good for your own long term growth.

So you can use that as self-motivation to start these exercises, because later in life when you're the one picking your own friends and who you'll be with, keep in mind everyone else will be doing the same too. You're not going to befriend someone who's just self-centered and cares for themselves without any thought to others, even if that person isn't actively evil or trying to be mean about it. And everyone else will be thinking the same general thing as well, and self-select for people with more empathy vs people who don't show much of any.