(stealing, since they have not asked the original singer’s permission)
AFAIK, it’s legally considered a parody, and is permitted. They may owe a small amount of money to the copyright holder, but so few copies of these album are sold, that the amount is very small, and the copyright owners don’t really care. Even if they do, not paying them is still not as bad as stealing, which has a much harsher connotation.