The use of transposed notation (writing notes higher or lower than they really are) probably started with the slow changes in how to make instruments. There was a "clarinet in C" when Mozart was alive, but was later replaced by the larger, richer sounding "clarinet in B♭". There was no change to how clarinet players had to move their fingers. That helped players change from the older instrument to the newer instrument. Maybe learners of the modern day instrument in B♭ could re-learn how to use their fingers, so they could play with normal notes. But all written music would have to be transposed back to "concert pitch".