I see that as a legit reason for Lautern. That area has always depended on U.S. military investment, and it's a small city in a mostly rural region.
But for Schalke? Nah. The entire Ruhrpott has gone through a ton of crap for decades now as they killed off the coal mines and all the industries around that, but that hasn't stopped Schalke and Dortmund from becoming the 2nd and 3rd club in Germany in terms of support and for a time also in terms of success. That club has just always been a bit of a disaster waiting to happen in terms of the club leadership.
But there's also a simple truth here that applies to pretty much every club in the league other than Bayern or the clubs with a safety net in the form of a billion dollar corporate sugar daddy..if you have to keep selling all your best players you may eventually end up in a situation where all the replacements you buy aren't nearly as good as the players they were meant to replace. It doesn't take much, 3-4 bad transfers and your team could be bound for the nether regions of the table.