Traveller in NZ here, what's with the driving?

Been living and travelling in NZ for just over a year now, and I genuinely don't feel safe on the roads anymore. I'm from the UK and whilst I feel most people are decent drivers there, there are a few problem cases here and there.

But honestly New Zealand has kinda scared me at times with it's driving. The amount of people I've had rush through to overtake at dangerous spots, sit right up my arse on 100 roads, stop suddenly to turn without indicating. Oh and the amount of times I have taken a milisecond longer to move off at a light and get horned, sometimes I'll just be driving normally and some cunt in a commodore or legacy beeps at me and swerves round.

Sorry for the rant but I am genuinely interested why road rage and bad driving is so common here.