The gap between players who've been playing OC since it came out and those who are new to it will widen over time, so I assume they decided to hide Job Mastery stacks to decrease the chances of newer players getting kicked from parties for low stacks once the content is a bit older. Alternatively, it could be to reduce clutter in the status effect list. Being able to see it would be mildly interesting, but I think the choice to hide it was reasonable. A completely silent CE party composed of the 7 people who coincidentally said "lfg CE" next to each other in shout chat probably isn't going to feel like a very social experience regardless. Though, I have still had a few entertaining social interactions in OC...mostly ones that involve dying while trying to Raise someone in an area with high level enemies.