Why not the same?
How come nobody has answered this?
The same reason you didn't, no one has an answer.
Same reason the frequencies where the stations are is different.
Tried looking it up but couldn't find any answer.
Mark
Looked further and found that using a 75US pre-emphisis has better signal to noise ratio but the 50US pre-emphisis allows a little more noise but better high frequency headroom. Only North America and N Korea use 75US and the rest of the world is 50US....A subtle increase in noise for better high frequency fidelity.
When FM started here in the USA programming was mostly classical and maybe jazz and the high end had to be boosted more because it was lacking and audiophiles didn't want to hear any noise in the quiet passages.
This 75US standard stayed unchanged.
But why on AM is the station frequencies different there than here? Having stations every 10 KLZ seems more logical than every 9 KLZ apart.
Mark
Thank you Mark for bringing an answer about FM preemphasis.
As for the different AM bandwidths, I am only guessing, but at 9kHz perhaps there's room for more stations, and I also think narrow bandwidth signals might go farther? Not sure about that last thought.
Yes thank you everyone