Among other things, the USB host polls the keyboard at a fixed rate. Fantastic breakdown if you have 30 minutes: https://youtu.be/wdgULBpRoXk

2.4GHz radio is faster than most wired connections - though the top-end ones with custom high-hertz implementations are slightly better than wireless.

Radio is also generally significantly more consistent - even when the polling rates are identical. You can see this if you look at the testing done by RTings for mice and keyboards. The latency when using 2.4GHz wireless is extremely consistent, while for standard wired connections, the latency varies drastically from input to input.

Bluetooth is crap and should never be used for gaming inputs. It's both high latency and inconsistent.