A motor, Delta bandsaw, has a name plate with the following information:

120/240 volts
1.5/2.0 hp
12.8/8.6 amps

For 120 volt use it appears that a 20amp circuit is required.

In reality the motor is

120/240 volts
2.0/2.0 hp
17.2/8.6 amps

Now, a 25amp circuit is required.

What prevents manufacturers of other equipment from "derating" their products to avoid the 80% or 50% rule.

I can see manufacturers selling a suite of kitchen appliances - dishwasher, disposal, refrigerator, and freezer, that all fit on one 20amp circuit.