In the US the guest is still expected to bring them, but as a host it's really nice to be able to provide for your guest if they need it.

This.

Plus, there are many emergencies where a guest wouldn't be prepared. For example, maybe someone who was coming for a couple hours to hang out/play games had their contact fall out. Or maybe a date went really well, and somebody stays the night who wasn't specifically packed for such. Maybe a friend needs last-minute emergency crash space, etc.