There are so many cycles on the country roads where I live that I can see how frustration gets the better of drivers, even those disposed to be considerate. It's not unusual to follow a cycle for say 1/4 mile and then, at what would be the first overtaking opportunity, to see two or three more oncoming cycles that prevent a pass.
I think most of it is ignorance rather than malice and those people, prompted to think about it and maybe made aware of why cyclists ride 'out' or abreast deliberately at times, are happy to take it on board.
In the days of quieter roads and slower traffic the default for many drivers seemed to be that cycles, if they stayed left, basically required no course deviation so could more or less be ignored as long as they didn't actually hit them. This persists I think with some older drivers - it's surprising how often the 'offenders' are mature people rather than young hotheads.
A good friend is an excellent driver in almost every way but a year or two back when I was a passenger with him he was quite impatient about a pair riding abreast around a series of bends. They were probably doing close to 20mph anyway, clearly experienced cyclists and I said "don't worry, they'll single out on the straight bit by the church" which they did. I explained why I would do something similar. He got it immediately.
Another chap I know well, with a very distinctive car, passed me at c. 50mph and facing oncoming traffic, staying on my side of the road and probably giving me perhaps a yard of clearance. At that speed of course it feels like a foot. I know him to be a laid back, thoughtful sort of chap and when I told him how scary it was (he doesn't cycle AFAIK) he apologised and took it very positively.
Of course there is a minority who are just sociopaths and they are the ones who need enforcement, not just education.
If possible I raise a hand to a driver who has waited to make a safe pass. We shouldn't have to, but thanks cost nothing and who doesn't like getting a thank-you? One who recognised me later commented on how unusual this is, yet horse riders almost always do it. Stereotyping of drivers or cyclists doesn't help.