So what reason is there to play Singed?

He seems viable in lower levels, but gets outclassed by everyone and is easy to play against if you're above bronze. The need for this champ to build AP and mana makes him squishier than most tanks and out damaged by most champs. Rylai's pretty much being the one redeeming feature of singed. He just runs around everywhere spewing poison late game if he can even make it there. Champs that would be vulnerable to your flips in this meta have some way to deal with it or just will avoid getting flipped in general. It's nice to get a root every once in a while with his E, but again most champs have some way of dealing with your flip as immobile champs become less and less common picks. Going into team fights he just gets destroyed from CC and can't do what he's made to do.