I doubt it’s for any intentional reason, but hypothetically if it were I would guess the reasoning would be along the lines of banning GDKPs doesn’t impact anything but those GDKPs, while interfering with boosting inherently restricts legitimate activities.
100% of GDKPs are tainted by gold buying, and their very existence encourages RMT. But there is tons of legitimate and non-problematic activity that uses the mechanics they disrupt to stop boosting. People farm dungeons for gold. People rush their friends.