Please explain pre-ordering to me!

I pre-ordered Rachel Hollis' new book, "Girl, Stop Apologizing". It was released yesterday. My book shipped yesterday, but I won't receive it until Friday. So, I could have gone to the store yesterday and bought it, but since I pre-ordered it, I won't have it until Friday. That doesn't make any sense to me. I mean, pre-ordering it did give me access to extra content, but I still won't get the actual book until a few days after it was released.

Another woman who pre-ordered it did receive hers yesterday though, she posted it on Instagram.

I'm just confused. Please explain this to me.