Why did the name Tasawwuf…

Why did the name Tasawwuf become used rather than Ihsan? One reason is, because we cannot or don’t want to call someone a Muhsin (i.e. he is very pious, pure, he has reached the pinnacle of purity. This is very ambitious, even arrogant). Also, comparing the other aspects of the Deen, Iman has evolved into the sciences of ‘Aqeedah, and Islam has evolved into the study of Fiqh.