Why wouldn’t they? Is the idea that a person can get any content a library might offer online (and for free, if willing to pirate it)? I can’t disagree with that, though if you’re not ok with pirating things then I think the value is enormous.
I think libraries are more than just the sum of the books, CDs, and DVDs on the shelves. In my experience they often have discounts to area activities (e.g., museums), offer classes and activities across the age spectrum (from story time for children to tech help geared toward the elderly or just the tech disinclined), and provide a nexus for community.
I think folks that haven’t been to a library in awhile would be pleasantly surprised with what they offer nowadays — though of course I only have personal experience with libraries across a few states in the northeast. It’s totally possible that I’m spoiled and don’t even know it.