Note that these are keyboards and not mouses, and they have USB-C sockets rather than permanently attached cables with USB-C plugs. They are also very premium products.
When it comes to the entire ecosystem, a $5 bargain-bin noname OEM keyboard with permanently-attached cable is more representative - and those definitely don't come with USB-C yet. That would probably add a few cents to their BOM, so it simply isn't worth it yet.
That is fairly meaningless, though. My six year old CODE keyboard could be USB-C today if I wanted, it uses a detachable USB cable. They wouldn't even need to make any changes to the keyboard other than including a different cable.
When it comes to the entire ecosystem, a $5 bargain-bin noname OEM keyboard with permanently-attached cable is more representative - and those definitely don't come with USB-C yet. That would probably add a few cents to their BOM, so it simply isn't worth it yet.