system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why aren't all instruments in Concert C?

It makes no sense to me that an Eb on some instruments is a C on a piano. Why would have we chosen not to standardize what tone a particular note is? Transposition is tough, is what I'm trying to say. So, please, somebody justify it for me (like I'm five).
gpt
Historically, it was common to have families of very closely related instruments with identical fingering systems but different sizes (for example, clarinets in A and Bb).
Players of one instrument would often play the other, but if all music were in concert pitch, then the player would have to learn an entirely new set of fingerings for an identical-feeling instrument.
It's not necessary to constantly transpose to concert pitch when you play a transposing instrument. However, if fingering systems were shifted around between identical instruments, it would be necessary to keep in mind which of many sets of fingerings to follow.
Hope that helps you. Please let me know if you need additional clarification.