Exactly. A consistently profitable trader would be stupid to focus his efforts on selling trading courses and books. Simple as that.
TA as it relates to day trading is more like giving a jackhammer to an 80 pound kid rather than a drill or hammer, especially the vague way many trading teachers sell TA to the vulnerable masses.
TA has potential when combined with other strategies but I have never been able to use it to consistently make money and minimize losses and I think a lot of trading teachers struggle with consistency in the long-term as well, due to the randomness of the markets. That's why they end up working on the side as teachers or going full-time as trading teachers and stop day trading.