I couldn't say why they don't for sure.....but, I can make a guess.
As the name suggests, the guide gun was intended for the hunting guide. He wasn't using the gun for hunting, but rather for back-up and camp defense. In these roles, the bigger the bullet, the better for maximizing stopping power.
The 444 is more of an offensive cartridge, having few choices for bullets in the real heavyweight range.
Probably wrong, but that's my guess!
hog
