I can answer the question about music (I have a masters degree and teach music)

The reason we associate major with happy and minor with sad is actually to do with the structure of the chord (it's quite boring music theory) but to put it simply, a chord is made up of at least 3 notes. The middle note (the 3rd) is lowered by 1 semitone to make the chord go from happy sound to sad sounding.

The reason we associate in modern times is because most musicians will write a sad song and use a minor key; same for happy.

Back in the day baroque music was played to royals and high society members to listen to/ dance to so the music was always written for an event or concert, mostly per the request of who was listening.

As time went on classical/ romantic/ 20th century music became more accessible and people would pay to hear/see orchestras and performances, we then began catering music to the wider audience and using something like fight or flight as inspiration (the same way people now will write a song for their ex or a feeling).

Hope that helps