@Frondeur Economy of scale, insurance, near total absence of paying work. It's inherently more dangerous, because planes can lose an engine and mostly glide for miles and pick out the safest area to put her down.
With a helo, your engine stops and you have to IMMEDIATELY do your autorotation and set her up to drift down safely. If you're absentmindedly looking out the window, this understandably goes poorly. That makes insurance costly, even more so when you're renting to people. So it's a vicious cycle: Pilots can't afford to fly and train like they want, making them less safe when they ARE flying.
It's also a smaller market, because there aren't many jobs for heli guys, and the military produces tons of qualified guys, so there isn't much of a training market to buoy sales and rentals.
Maintenance is harsh, piston engines aren't a great choice for a helicopter, but turbines are too expensive. I think the cheapest one out there is taken from the chinook's APU, the T55? That's a $500,000 helo if you're willing to build it yourself in the garage. The government wants to help owners (i.e. the guys renting YOU an aircraft) by forcing them to take care of maintenance and maintain it to a safe standard, so you have extra inspections (shop hours) and parts replacements on a schedule.
I said upthread that the R44 overhaul is around $200,000, and I'm probably lowballing that too. I don't know anyone that's done an overhaul on a private helicopter, probably because it's so much money.
Anyways, you have to overhaul all that stuff at ~2,000 to 2,400 hours, fed mandated because that's the most cost-efficient timeline to give you good operating life without parts failure (death)
It's like an economic death spiral, and that's not even touching on the cost increases from lawsuits over the years. Many wrongful death suits through the 70s/80s/90s that really hammered the industry