Because an accurate signal will never hit the market. What will hit the market are vague signals that are sold at a premium. These signals are coming from people who are not even experts themselves. These are people who are failing in trading even after they studied a lot about crypto trading. And to save these skills from becoming a total garbage, they are selling signals that are not really going to take place.
Most of these signals are just b.s. being sold to people in order to clear up some bags the people running it are holding. It's pretty simple really. Let's say that they bought too much XSN(just an example here) and the price went down and hasn't recovered for a few days. So, they post a signal telling everyone to buy XSN and put in their sell order to make a little profit off of it. You're the ones stuck holding their bags in the end and more than likely aren't going to make your money back off of that trade for a while.