So a VGA/component cable only works one way?
A VGA/Component video adapter cable is not an ACTIVE device. That is, there are just wires connecting two different types of ends, the signal that is on the cable remains the same.
An analogy:
You have a car that runs on gasoline only.
You also have diesel fuel.
What you are asking is if you pour the diesel (component), into a container, and write gasoline on the side, it will turn into gasoline (RGBHV). That's not the way it works!
Instead, you must push the diesel (component) through a conversion process that turns it into gasoline (RGBHV) - in our world this is called transcoding.
OR - you must have a car, with only one gas tank, that accepts either gasoline or diesel fuels. (this is common with many displays these days)
WHAT ABOUT USING THE CABLE THE OTHER WAY?
A computer spits out RGBHV video on a VGA connection. See the pinouts below, but it it works out to 5 separate coaxial cables that make up the video from a PC. The VGA/Component cable only has three cables on the component end and they are connected to red, green, blue, red ground, green ground, and blue ground on the VGA end. There is no provision inside to connect, or allow connectivity between H/Sync or V/Sync. OR - to change the video from RGB color space to component color space.
The solution to this is to have a computer with a video card that can be changed to output component video on the VGA port. If this is the case, then the computer is not going to use all 9 pins necessary for a RGBHV connection, but will only be using the 6 pins necessary for component video and will put the video in the component video color space.
Great graphic below shows all the pins and what they are used for on a VGA connector. Of the 15 pins, only 9 are necessary (I believe) for full bandwidth RGBHV. The others are additional PC related data.
Hope at least some of that made sense.