They could also just make all those compatibilities non-optional. Problem solved.
Want USB 2.0 but not USB 3.0 or 4.0? Just put a USB 2.0 port on the damn device.
Want USB 4.0 but faster? Name it USB 5.0. USB 1.0, 1.1, 2.0 all used the same plug and nobody is confused about that. Same applies to USB-C and USB 4: either you implement it (fully) or if you don't want to: implement legacy USB instead.
Maybe we should have thought of that ahead of time. USB-C with USB 3, 4 and Thunderbolt just pushed us back into RS232 DB-9 territory where the plug doesn't mean anything anymore, and while a lot of things might physically fit, you won't be able to predict what's going to happen, or if anything will even happen at all.
That cheap cable probably also has an even cheaper variant that simply sets itself on fire if you put more than 10W through it. And that variant might only support USB 2.0 and as such transfer speeds are so bad people now have to think in terms of 'which one was my slow cable'.
If all cables had to be complaint with all features we would see economies of scale that are never going to happen in the current market.
The high speed cable might never be as cheap as €7, but in a couple years it could be €9-11.
I'm sure at some point high speed cables will be a lot cheaper than they are now, but as long as the make up a small percentage of the market they will command a big premium.
Want USB 2.0 but not USB 3.0 or 4.0? Just put a USB 2.0 port on the damn device.
Want USB 4.0 but faster? Name it USB 5.0. USB 1.0, 1.1, 2.0 all used the same plug and nobody is confused about that. Same applies to USB-C and USB 4: either you implement it (fully) or if you don't want to: implement legacy USB instead.