Why is CAT rating not applied to switches?

Solution 1:

CATx are physical cable wiring standards, specifying physical wiring characteristics of the cable, like impedance, number of conductors, twist rate, etc.

Switches do not care about the physical properties of the cable. All they care about is whether or not the cable is able to successfully transmit data. It is assumed that cabling used will be within spec for whatever speed/duplex that is required, and depending on what speed uplink is required, there may be any number of physical cabling types that will work fine.

An analogy would be high voltage wiring, such as 12-3 romex. That describes the physical properties of the cable, not necessarily what it's going to be used for. 12-3 romex is rated to ~120v @ 15A or thereabouts. The wall sockets that 12-3 romex is terminated in are not called "12-3 romex sockets". They're called NEMA 5-15 sockets. It is assumed that the cabling terminated is up to spec.