Because when Google finds out about a website working on blackhat techniques it simply penalizes it. Therefore blackhat techniques only work on the short term and if you want to earn money fast, but not on the long term.
certainly the most important thing about this technology is the use of signals that may ultimately be either picked up or overlooked by google. at this point, all the rankings will simply vanish nd switching domains will turn out to be highly costly.
Short term black hat SEO works fast because it tricks search engines using shortcuts like fake links or hidden text. However search engines constantly update their systems to catch these tricks and will penalize or drop your rankings. Eventually your site loses all its traffic because it lacks real value for users.
