Why do Americans avoid a simple grid to divide their voting districts and public elections?

A grid doesn't work. Constituency boundaries have to be regularly reviewed so as to keep all constituencies roughly equal in population.

Here's a link to the independent public body that does it in England: https://boundarycommissionforengland.independent.gov.uk/about-us/

The US has no such commission, instead they have political appointees who do it with the result that the boundaries get drawn so as to favour particular parties. This is called gerrymandering, see https://en.wikipedia.org/wiki/Gerrymandering.