Why doesn't single user license lock playback to a single device?

[jimmynitcher]

Hi, why does Spotify allow a device to be hijacked under a single user license, it's under my name but my daughter can log in and use it and it turns me off even if I am on it first,  why would it go off at all if it is only intended for one person? It seems her device takes priority from then on. 

I would hate to think this inconvenient implementation was to encourage me to pay for a family license!

If she is breaking the license agreement by logging into my account then why is it possible at all?

Thanks