Random artifact powers is an idea from back in 1E that carried over into 2E. As far as I can tell, the design philosophy was that artifacts (there were no minor artifacts back then) had one or two signature powers, and the rest were randomly determined by the DM at some point so players who found one wouldn't immediately know everything they did, giving DMs some room for mystery even if the players had read the books.
3E saw a change in the game design philosophy. Having the nature of powers be determined randomly was now considered to have too much potential to wreak unbalancing havoc, and didn't reward or punish the player/DM enough based on their own resourcefulness (hence why there are no WotC-published Wild Mages anymore). Random artifact powers are gone.