Because investing can be harmful.
If we are talking about bitcoin investing, then it is not harmful at all, bitcoin has always been growing historically. It is better to invest in bitcoin than to trade it.
*Yield farming (De-fi)=
You can do this easily by following some rules. There are many tasks to do it in many boards. You can earn it by following their rules.
As a person who was closely involved in token farming, I can say for sure that this is not easy. You need to know some of the nuances of working with a swap token. And it is also very expensive, commissions sometimes go through the roof and can gobble up almost all of your profit. I highly discourage beginners from farming, especially without proper balance and not chasing high APYs.