Why is it so?

That’s the biggest question of all, eh? The answer truly depends on what your "it" is. Are you asking about a law of physics, or maybe a social issue? Every "why" has its own specific explanation. It could be simple cause and effect, or it might involve complex human behaviour. If you can provide a bit more context on the subject, folks here could probably give you a much more accurate answer. It's a tough one to tackle otherwise