The vast majority of my observations come from my dedicated camera and I use third party software to geotag my photos from a GPX track. Unfortunately the geotagging doesn’t add horizontal accuracy data, just coordinates, so most of my observations lack any horizontal accuracy data. Any horizontal accuracy I add to them would just be a guess and I agree with @pisum that this isn’t necessarily an improvement. I think emphasizing it would a) reduce the number of observations being added because of confusion and it being an extra barrier and b) pressure people into just adding something without thinking much about it.
In my experience (and I could be wrong) most observations with incredibly large accuracy circles come from mobile app users and I honestly can’t figure out how they get those.