why don't people say mega meters

https://lemmy.world/post/12883540

why don't people say mega meters - Lemmy.World

How come people say 5,000 km and not 5 Mm? why not just say millions of meters or Mega meters?

Familiarity I guess. Mega isn’t really a widely used prefix outside of computers. We even say tons instead of megagrams.
megaton, megawatt, megapascal, megacandela (for military flares), megahertz, megajoule, megaohm, megabequerel
Megatron
That’s a lot of Trons