Because it could lead to all manner of weirdness that the user doesn't expect. Imagine someone trying to type some data into a spreadsheet and every time they hit the capslock key a strange text string appears in the cell, maybe leading to data corruption. Or even worse, it happens in some program where the typed characters are interpreted as hotkeys and instantly perform some unknown combination of actions which the user may or may not even know occurred.

He failed to consider that people on hacker news would tut disapprovingly at his hack.