Because root is what you find on the bottom of a plant or tree. Route is the highway you take such as Route 66. Please reread my prior post in the US a fender is what you call a wing. We call it a bumper you call it a fender correct?
I think Winston Churchill said it best. Something to the effect, ( English and Americans separated by a Common Language).
I did look it up in the dictionary and route is pronounced root in the UK and rowt or root is acceptable in the US. You got to keep in mind the US is a big place with different dialects. Kansas by itself is 82,278 Sq miles with a population of 2,911,505. The UK is 93,627 Sq miles with a population 66,435,600 million