Somebody integrated ShellCheck into Google's code review system about four years ago, right before I left.
So the result was that every code review I sent with a shell script was filled with red squigglies -- "add double quotes here". Most code reviewers don't really know shell, but if they see red squigglies, they will say "fix this".
The double quotes are of course technically correct, but when you're writing a shell script in a subdir 8 levels deep in the repo that only operates on 3 files in that subdir, it's overkill and makes everything ugly.
In other words, it was the typical "static analysis has annoying false positives" issue.
Most of the shell scripts I write deal with "trusted" filenames -- i.e. those checked into the repo. If you want to deal with untrusted filenames, then there are a lot of ugly techniques to do that.
So Oil is basically meant to make the default thing the right thing, and the common thing the short thing (Huffman coding, as Larry Wall calls it).