I think because that was the style. I couldn't get it to stay tied behind her head.
If you pull her hair back in a pony, and then tie the hat ribbons first around the pony and then under, it works better. Takes a bit of adjusting to make it look right.
I do love this hat. Granted, it does not stay on solidly through much play, but for display purposes it is fine. The brocade slippers are very well made and never slip off, which is also a bonus. The entire set gets an A- from me.