It's because, as you well know, the circling mins exist to provide obstacle clearance for the TERPs protected lateral distance provided to airplanes per their approach Category. As a helo, I'm not utilizing that circling airspace.....not flying a pattern to land, hence, I can make a ILS to Runway 9 for example, even though Runway 18 may be the duty runway at the time, and I break out at straight in mins and if I'm a light helo, air taxi over to the ramp, pad, taxiway, wherever. Or if a medium/large wheeled helo with a lot of downwash, air/hover taxi to the designated runway or taxiway, turn into the wind in place, and land. So it really makes instrument approaches easier in terms of the landing phase of the final segment.
In the same way, for non precision approaches, VDPs don't apply to helicopters. Since I can level off at an MDA, and drive forward all the way past the VDP, still spot the airport/runway all the way up to the Missed approach point, and still maneuver down to land, straight/turning, etc. I don't need the glidepath that the VDP gives, because I'm always in a "position to land" all the way up to the MAP, whereas airplanes aren't.
So there's some convenient things helos don't have to worry about as it comes to instrument approach work, that airplanes have to.