Why are most older siblings so mean and brutal to younger siblings?

My brothers were mean to me. This is when we were kids. I was mean to them too. My oldest brother told me, "You need to learn to respect your elders. That's why I'm so mean because YOU'RE being mean. Would you like if someone got into YOUR face (gets in my face) or push you for no reason? Do you like that? I said no. I was a kid at the time. Then he said, "Well respect people! Otherwise they're going to be nasty back." I was a HUGE brat and my brothers weren't afraid to out us in our place.
Why are older siblings so mean? Older siblings please explain.