Two main points:
- no one unified distro to keep things simple (thread OP)
VS
- people don’t care. Someone else needs to advocate, sell, migrate, and support (medium term) Linux (whichever distro they want) for the intermediate term (few months at least) - thread response).
I think a lot of the 97% desktop market share is like this, instead of the hands on 2-3%.
You’re basically describing the Linux Standard Base, which was abandoned back in 2015 and the way it was handled was somewhat controversial.
But there is a lot of informal standardization between Linuxes, nonetheless.