If you think suicide is selfish, then maybe the world should stop beating people down in general to the point that they have to look within themselves to feel refuge. You're clueless as it gets.
I don't think you've truly been in a situation where you really wanted to end it or you'd understand that it's anything far from selfish. Some people who've been there actually feel that the world and everyone around them would be happier if they were not a burden on them. You have it completely twisted. Some are actually thinking about others and calculate (often tragically miscalculate) that their death won't make them less of a burden but it can be hard to convince someone of that when they've been told all their life that they were useless or a burden or told that they got on their nerves from multiple people around them.
Some people are naturally shy and introverted and as a result it may be hard for them to know that not everyone is the same as those who have hurt or judged them in the past. So they see everyone they encounter as a problem or think that random people are judging them the way their parents or older relatives judged them.