The cable is more than just a cable, it has a microcontroller that handles the car's diagnostic protocol.
The software on your computer talks to the cable with a proprietary protocol specific to the cable's manufacturer, and the cable itself translates that to the car's protocol equivalent.
I've actually wondered why we can't have a single cable for all cars and handle the car's protocol on the computer directly (the cable being a simple converter that relays frames received on the car side to the computer's side and vice-versa), and here's a reply I got from Ross-Tech (the VCDS developer) :
A "dumb" network to K or CAN converter is not a practical device; diagnostic protocols are too demanding of real-time responses from he device that's interrogating them.
Apparently the latency induced by having the CAN packet going to the computer, being processed there and going back is too much, that's why it's needed to handle the car protocol directly on the cable.
Implementing OBD-II is simple and that protocol is standard and most likely open. Implementing manufacturer-specific protocols is hard because there is very little documentation about them and the only way to know that protocol is to reverse-engineer the firmwares of the ECUs or to capture the communication between the car and the manufacturer's official diagnostic device. So it is hard, time-consuming and expensive to do that for the protocol used by each manufacturer, and then implement all of that directly on the cable's microcontroller.
Still, there are universal cables, they're just extremely expensive (most likely for the reasons I mentioned above) and I doubt they have all the features that the manufacturer-specific tools have (it's not only about the diagnostic, the cables you mentioned can configure the car, for example add new keys or tweak the steering assist).