And those are great, they really are, if you happen to be playing at a time when people are doing those runs, and there’s room for you in those groups, which is not always the case.
The reality is that some people simply prefer to run LFR as their chosen content, and they have zero interest in exploring any difficulty modes higher than that, whether it’s because of their real life schedule, their physical ability to play, or just an unwillingness to really go beyond what they consider their ceiling when it comes to content difficulty.
This wouldn’t even be an issue if Blizzard had made their stance on the slime cat clear from the get go. As Tovi pointed out, saying “Hey, you can get the slime cat on any difficulty.” until 2 days before the event starts, then saying: “Oh whoops, except LFR players, nah, you get nothing.” is not acceptable.