Probably because most Tahm Kench players, like myself, have basically given up. We recognize that Riot created a champion that is either extremely overpowered at high levels of play (i.e. high team coordination) or balanced based on pro play and thus does very poorly everywhere else. Riot realized that they can't allow him to be viable if they hope to see "#biglcsplays" because his role is inherently antithesis to their philosophy. Make no mistake, anyone who plays the champion in solo queue is handicapping their team. They can be the best Tahm Kench in the world but the champion just doesn't bring enough utility to the table to influence the game when the teams are evenly matched (i.e. teamfights).
I have stopped playing him in ranked because if I want to climb, I have to use someone else.