That's because it's none of your business. :lol: It's not up to use to determine whether a circuit is CL2 or CL3 or even Class 1. The class will be indicated on the power source as determined by the manufacturer using some mysterious testing method. If the information is not indicated we are to assume it's Class 1.
Those 150 and 300V voltage ratings relates to CL2 and CL3 listed cables respectively and they are only the voltage rating of the cable, nothing to do with what the actual voltages of CL2 and CL3 circuits may be. However we are not supposed to know that either. Notice it's not printed on the jacket, spool or box? You can find the voltage rating if you look up the specs for a specific cable but that is for use only if you are using it for a non NEC application.
-Hal