Penguins don’t have a strong supporting cast.
You have some aging stars in Sid, Letang and Malkin, some good players that aren't playing up top potential like Guentzel Rust and Murray, and a bunch of average younger players.
You add that to this teams tendency of overlooking opponents and this is what you get.
Even if they do manage to win the series they stand no chance against some of the other teams in the East.
Another problem I think many overlooked is how teams would react to the layoff, the new playoff format and being in the "bubble" playing without fans, in the same location etc. It effects teams and works for or against them differently IMO.