If rustfmt were not configurable, it would get a lot less use. Rust has been around for quite some time now, and there's a lot of code out there. We can't force anybody to run rustfmt, and if they don't like the results, they won't use it. It's not a choice between different code styles and a single code style; it's a choice between different code styles with a tool to keep things tidy and different code styles with a tool nobody uses. Things were different for Go for a variety of historical reasons, one important reason being that gofmt existed early on.

To take a concrete example, adopting gofmt's choice to not have a line length limit would have been a nonstarter, because lots of code out there uses long expressions manually wrapped to be readable. A lot of the work in rustfmt has gone into playing nicely with community conventions like these.