Nocturne's really good in soloq (easy post-6 kills and people tend to be bad at positioning/communicating). He's not picked in pro play because competitive junglers need to be able to provide a lot of pre-6 pressure (something Nocturne doesn't have enough of to be considered Elise/Gragas tier) and not require a ton of farm/gold to do well. He does quite well with items, but if he's not hitting those powerspikes (less farming in pro play) he won't be very useful because all of his nondamage utility lies in a two-second-to-proc fear and 4 seconds of vision (potentially very powerful).
People just don't play Nocturne in soloq (???) because no idea. You can use champion.gg for plat+ stats on champ picks, ban rates, win rates, etc or lolking for more low elo stats