Q: I have added drivers into my Windows PE image for my OS installation--so why aren't the drivers  available and why does my installation fail, saying the hardware can't be seen?

A: The boot.wim file actually contains two separate images, as shown below:

PS C:\windows\system32> dism /get-wiminfo /wimfile:d:\temp\boot.wim

Deployment Image Servicing and Management tool
Version: 6.3.9600.16384

Details for image : d:\temp\boot.wim

Index : 1
Name : Microsoft Windows PE (x64)
Description : Microsoft Windows PE (x64)
Size : 1,259,685,118 bytes

Index : 2
Name : Microsoft Windows Setup (x64)
Description : Microsoft Windows Setup (x64)
Size : 1,356,525,607 bytes

The operation completed successfully.

Typically, you mount the first image and add your drivers. The problem is that Windows actually boots from and uses the second image, not the first. This means you need to inject your drivers into image 2 and not image 1.