Why do carts, sites, whichever and zencart continue to support the imperial measuring system?

FACT: TWO (2) Countries on this entire planet Earth Use Imperial. US & Jamaica!

Wouldn't it be logical in every sense to use only metric for any and everything until the US catches up with the rest of the world? (if ever)

I.E.. Effectively 3.8 billion + people need to default to US (whatever population) measuring when using most software.

I thought there was a Brit on the major development team?

Until whichever day, if any the entire planet needs to convert the US measuring system (which the rest of the planet coped quite well with) and the US version of what they like to somehow call English spelling? More like phoenetics to the rest of the world.

Not a bash on US, but a logical solution to LIFE.