They are not scalpers looking for a few ticks. It is possible to follow them on the 15 min charts if you are a day-trader, there are at least more than 50 different financial instruments to choose from (in the US, UK, Europe, etc...)
I attempted to find original articles that detail this fabled "90% failure". Only 1 article - based on traders from India, gave sufficient details and data - their failure rate was 78% but even that one paper was clumsy and weak. I could not find any detailed studies or data to show "90% failure". Just saying.