QTR continues to be used by a small group of dedicated monochrome printers. Many people also use Lightroom as both processor and catalog. To print from Lightroom to a QTR profile that profile has to be made using the QTR-Create-ICC-RGB script. Lightroom doesn’t understand the grayscale version of profile. Lightroom, like most image processors, is written only to process RGB.
The digital image is in color.

Just as digital prefers daylight, digital prefers color.