I'm not a EE. It is my understanding that to fully test 24 pins would includes putting a full load of higher wattage through those wiring to ensure they are capable of transferring. Higher wattage which means it needs a larger transformer to output that large amount of power or it would need a 200+ watts power brick to supply the wattage. That includes needing safety/failsafe components to protect itself and the device it is connected to, thus increasing the risk of potential damage if it was mishandled. I won't be surprised if the cable reporting that it can handle higher wattage when it is not in reality. Also, this includes the testing system to ensure it is handling rigorously without damaging it.

I don't know the cost of the such device, I am assuming the higher cost based on other devices for other thing such as ethernet cable tester such as Fluke which are $100+.