If there would be enough demand to pay for it, it would stay open longer.
Gotta travel 20 miles to downtown for anything resembling night life.
Here's a line from my local library's site:
> Our auditoriums are provided as a public service for use by individuals, institutions, groups, organizations, and corporations for a small fee, when not being used for library-affiliated or sponsored activities.
Also if it would become really crowded they would probably think of prolonging opening hours.