Some time ago the powers that be determined that sassafras was carcinogenic, and the ingredients of root beer were 'sanitized', some chemical was substituted to give the sassafras flavor.
File, being in the sassafras family, was tarred with the same brush, but folks in Louisiana decided other things would probably get them first, so file gumbo continues on its way.

Genuine root beer with sassafras is still available at organic stores.