It wasn’t enough just to ask customers to wear masks. Part of the reason is how political masks have become, although I wonder if they’re getting less so as people become used to the requirement, the President wears one in public, and Red States are requiring them too.
There are subtleties in airline mask policies, but largely there’s been a six-part progression to airline rules. The latest is to define what kind of mask is acceptable. There’s an exception to the ‘no masks with valve’ rule, though.