[sannee]

Firstly, hardware debouncing is a bit awkward to implement on a multiplexed matrix, since you need a debouncing circuit for each of your inputs (meaning about a dozen or so of them).

More importantly though, software debouncing offers greater flexibility. For keyboards, you usually[1] want to implement an asymmetric "eager" mode, where a key press gets registered immediately and only the key release is debounced. Since software usually does stuff on the key down event, this works to reduce latency.

[1] Well, that's what the various enthusiast mechanical keyboard firmwares do, I am not so sure that generic $random_corp keyboards do care...