The reasoning of tempos

I was in my piano class in college and i was thinking why are tempos are so important with the speed why is hip-hop at the tempo 80-98 why most R&b is 54-78 bpm and it hit me why it is so important that if ur in the studio with sumone and there not as quick with there vocals or there are slower rappers its important to pick what rite for them if you look up stuff for sum singers and rapper they and do there thing in set tempos i know everyone here knows what a tempo means to a beat and speed but what does it mean to a song i remember awhile back i was in the studio with a guy and i had already made the beat and it was pretty much set but he liked the beat but the tempo was very bad but he had sum raps written so we made our way around it since now im in the choir and im singing it means everything I seen sumthing were mystro said that people arent looking for beats there looking for songs and i seen were a few A&R said it to if you have sumthing written to it it's eazyer to build around than sumone that has a beats set in stone and you having to work around the beat so i just wanted share my thoughts if you have anything to add plz do so

yeah if you remix a song you have to adjust most often to suit the tempo, not everones flow fits the same tempo or rhythm for that matter.