It's because they can basically move per data per second ona. busy cell site. A cat4 can move 1 slot per second, a cat12 4. Tht means on a busy cell where you can't even stream radio, a cat12 one probably can.I don't get why there is a need for those speeds. Personally I only want to stream Netflix, pickup emails and do a bit of internet surfing. Theoretically Netflix needs 3Mbps for standard viewing, 5Mbps for ultra HD 15Mbps I suppose it's more about picking up poor signals.
A cat20 5g unit is in effect able to combine both 4 and 5g radios too, so gets way more than the 6 basic slots you would think from the spec. We've had faster than home fibre broadband speeds in fields.