It is definitely terrible advice. It sets people up for a long investing career full of behavioral errors and vain attempts to beat legions of people and machines better than you at actively trading.
I believe you are underestimating the perceived complexity in investing by people who don't understand it at all. I also believe you are underestimating the amount of diversification that a dozen stocks chosen from different industries can provide. It's better to start sub-optimally than not start at all.