This has nothing to do with the Cat not being available in LFR. It’s about the way Blizzard handled this. Here, I’ll copy paste what I put in other threads on this topic:
The issue isn’t that LFR players aren’t getting access to the slime cat mount, it’s that Blizzard yanked the rug out from under LFR players by making them think they could earn it until a few days before the season was due to start.
If, from the get go, Blizzard had said “You must complete the fated raids on normal difficulty or higher to get the slime cat.” no one would have given a damn. Sure there would be some players who would ask for LFR to be included and raise the question as to why LFR players were excluded but there wouldn’t be the anger we’re seeing now.
This mess is entirely Blizzards doing and they should fix it before S4 goes live by making it possible for LFR players to earn the mount, which they didn’t say wasn’t possible until a few days ago.
By the way? As of right now the in-game achievement panel still implies that you can earn the slime cat mount if you do LFR. It has NOT been updated. So players who do not pay attention to the forums or any news posts and do LFR content are going to be PISSED when they complete all the fated raids on LFR and don’t get the reward the achievement says they should be getting.