Almost all rotary switches have a stiff disc wiper made out of a different material to the springier metal that the leaf/leaves are made out of.
'Almost all' *but not* all. I can think of several off the top of my head that use similar metals and some of those are not even 'high end' parts.
This is for a control going in a PAS-3 or similar circuit. If the values are not observed there will be a price paid in the form of bandwidth.