They haven't developed any players under Sullivan's tenure. Keeping him around because "nobody can fix it" makes no sense.
If the roster is as bad as the performance you are going to get high draft position regardless of coach and with Sullivan your young players are going to get 6 minutes a night so Matt Nieto and Kevin Hayes can fart around doing nothing.
How can you develop players when you treat them all like 4th liners? Hell even Jake Guentzel he treated like a 4th liner, but Jake was on a team that was in a far more positive head space after winning the cup the year before and just an absolute machine, he had him with Cullen for parts of his first season if you remember.
Since then, he's treated them all like 4th liners or at best if they're super lucky, 3rd liners - McGroarty, O'Connor, Puustinen, Poulin etc. Then some he wouldn't even play past the 4th line or much at all - Hallander, Gruden, Ponomarev, Lafferty, Angello, Bjorkqvist, etc.
Or they'd just marinate forever in WBS and leave. I still laugh at how much of a piece of shit he was with players like Friedman, POJ, Riikola, etc. He just pouted having to use them and would throw them in usage to purposely sink them and when Ruhwedel was also shit he'd still play him anyway while the others were held to some ridiculously high standard that wasn't the same for others. Do these names matter? f*** no, the situations do. Everyone wants to focus on the f***ing names and then attach their bias towards "well he sucked" who gives a f***.
Look at how he used them. He would play them to so they fail and he could then say see, told you.
Look at the rope Rust (and even Simon and Sheary) got to develop and keep playing through his mistakes, he only got that because he was with Sullivan in WBS.