Cousins are a really great way to be around role models who are in a next phase of life.
Siblings are usually too close in age (or younger), parents are many many steps ahead and experienced your current phase in a different world. But if you're entering high school it's useful to have a connection with people entering college, or getting their first job. That rarely happens outside of the family.
That’s a function of smaller families and parents delaying children until ~30+, one of my siblings was in collage when another was born.
Sure that’s an unusually wide range today, but if you trace family trees you can find many examples of aunts and uncles who are younger than their nieces and nephews.
Siblings are usually too close in age (or younger), parents are many many steps ahead and experienced your current phase in a different world. But if you're entering high school it's useful to have a connection with people entering college, or getting their first job. That rarely happens outside of the family.