Because a GDKP is a service of sorts. People have to pay in to those, or they make substantially more gold than a regular raid run. Advertising for those ONLY go in trade chat. And because it is a service of sorts, it’s not against the ToS. But it is a service to make gold or potentially purchase gear. It may not be an outright carry, but it is still something you’re advertising that does not belong in LFG.
Regular run of the mill groups to run raids and dungeons - those are the absolute ONLY thing that should be in LFG. It is not a global trade chat. It is not a global Barrens chat.
Someone else had posted here over the past couple of days, though they were silenced rather than suspended. You can look that thread over for all relevant posts and data.