He just needs a Riot™ rework. Playing around him is a pain for everyone.
but when was the last time you even SAW a Singed? Chances are not very recently, and I can almost guarantee it was a stuffty Singed that did nothing useful.
Singed gets no love because people don't play him and riot doesn't make much money from his skins because of the first point.
Singed is in a really bad spot right now, being literally unplayable in high elo and competitive play while not being particularly good at any of his jobs.
He has good wave clear but horrible split because he takes down towers so slowly.
He has a good level 2 but an absolutely stuff early game that lasts until he gets 3 items minimum.
He has a good late game but it isn't made up for because he's kiteable as forget and hard cc = dead
He has an interesting kit that is constricted by long cool downs and high mana costs, and his passive is completely useless and doesnt provide any real incentive to buy mana because Singed needs those slots for tank items and rylais/liandrys.
Basically, there is NO REASON to pick Singed unless you love his design and playstyle because other champions do what he does MUCH better with less knowledge and experience required.
You'll see much higher gains from playing Gangplank or Irelia than Singed, with so much less knowledge required, as well as both being less weak to hard cc than Singed is due to GP oranges and irelia's tenacity, while also offering some kind of alternative damage so they don't get completely boned by resist stacking tanks, as well as having a better time farming in turret than Singed could ever dream of, and cc that is MUCH easier to land than the fling glue combo.
Tl;dr don't be fooled by singed's winrate, it's artificially inflated by a bunch of try-hard die-hard Singed mains because nobody else plays him. His cool downs and mana costs are oppressive, his passive sucks massive rooster, and other champions do what he does with less time and effort required to learn them.