Nobody plays him anymore because he's awful top lane, mediocre as an ADC and hit or miss at mid. He was supposed to be a top laner, but as of now he can't even out trade meta toplaners despite being one of the most immobile champs in the game. There was a point in his life were he countered almost every assassin(old morde at least), but the damage has become so high now that these champs can just burst Morde down before he can do anything.
His base health at 18 is 1856. For a juggernaut, that is absolutely laughable when Darius has 2200~ and even some champs like Fizz have 2200~ base health at 18 while being mobile and bursty. Jhin, a ADC, has 2103 hp and outdamages Morde's whole rotation late by right clicking a couple times from a super far range.
Morde's rework was supposed to make him an ADC replacement somehow, but he falls off after 20-25 minutes harder than almost any champion out there due to his lack of tankiness and immobility. You can argue that he's an "earlygame ADC" but his early is actually crap and he shines the most at mid when fed, which wont matter at all if you lose lane or go even.
He needs some changes. Yeah, I get it, not many people play Mordekaiser, but some minor changes to make him more fun would be nice for those of us that do while we wait for his VGU.