I think most do just need a warning. Quite often they are plainly not aware of how much room they need to allow or are just unable to judge it correctly. And then there are those that think they own the road - I have a couple of narrow one way roads on my commute where it isn't actually possible to pass. These are always quite contentious and I've lost count of how many MGIFs (must get in front) and left hooks I've had. Another common theme is car drivers misjudging a cyclist's speed. Seeing a bike seems to get immediately interpreted as 'slow moving vehicle' when I'm certainly not most of the time!
Road.cc carries an ongoing daily news articles on their near miss if the day. Pretty sobering viewing at times...
https://road.cc/news