Maybe because backtesting can give you statistics on the probability of you being right or wrong. You can then use the stats to either take the trade or not take the trade...providing you with more in-depth info than just
"market is yelling to you". In addition, you can use the stats to help you determine your position size management, stop loss placement and many other things that's useful in trading.
Without that info, the market yelling at you may be just too risky for people to listen too especially for those that want more info to give merit to the market is yelling at you.
For example, what if someone saw that the
market is yelling at you before you saw it and they did it via having statistical data ???
I'm not judging but some folks use stats to see things that others have
yet to visualize on their own or have yet to hear. it on their own. They hear or see what others are saying and then they backtest it to see if such is true or not true.
P.S. I read a stats guy say the same thing as you just did back in February 2018 while others having been "screeming" the same thing back in the fall of 2015.
wrbtrader