I want to take her on a graduation trip, but why can't people under the age of 18 stay alone

The main purpose is to protect the safety of minors. If you are under the age of 18, you may only pay attention to smaller hotels, or express hotels and youth apartments!

This is a national law to protect the personal safety of minors, and at least one adult must accompany them to check in. Welcome to click "Adopt", not "Useful"

Two over 18 years old, should be ok?