I think vi mode suffers because it's a relatively niche feature - none of the current committers use it as far as I know, and pull requests to improve it are fairly infrequent. It gained t/T/;/,/d{f,F,t,T} in 3.0 in two different pull requests, which represents about 1% of all PRs in the 3.0 cycle.
I don't think it helps that it's this huge target area which (the small number of?) users use a slightly different 10% of, and it can be quite complex to integrate new features into existing editor state.
I don't think it helps that it's this huge target area which (the small number of?) users use a slightly different 10% of, and it can be quite complex to integrate new features into existing editor state.