What prevents someone from checking an ID against a central-authority? I mean, doing so online isn't necessary -- there're plenty of validation mechanisms that

What prevents someone from checking an ID against a central-authority? I mean, doing so online isn't necessary -- there're plenty of validation mechanisms that could work offline, and presumably they'd be useful in the odd cases in which internet-connectivity isn't available. But internet-connectivity tends to be pretty accessible in most scenarios where an ID would need to be checked anyway, right?