Have the pens struggled filling the stands? I don't remember this being a thing there
Any time they start losing and the economy is less than great, they stop filling seats. Remember, the Penguins' fanbase has been relatively fairweather historically, plus the local economy isn't the most stable, thus less disposable/discretionary income on a consistent basis.
Western Pennsylvania has lost a ton of people since the late 1970s as a result of the steel industry collapse, so that along with the fact that very few people move to Western PA, both domestic and immigration, means the local population base has dwindled. It's a Steelers first market, Penguins do very well when winning, and the Pirates (like most baseball teams now) are a summer thing to do, but that fanbase has tuned out due to ownership.