(Also, it's not like ARM was a single instruction set before either. For quite some time ARM had two totally different instruction encodings, the "usual one", and Thumb2, with microcontrollers usually only supporting the latter.)
(Also, it's not like ARM was a single instruction set before either. For quite some time ARM had two totally different instruction encodings, the "usual one", and Thumb2, with microcontrollers usually only supporting the latter.)