I think it comes down to economy, right? There have to be revenue streams for any town. For some its manufacturing, others tourism/entertainment. Some cities and towns are tech-hubs, travel-hubs, etc. If you have a population of 5000, call it 3500 working adults, you need 3500 jobs that pay living wages within an hour or two, whether that is something inherently bringing value to your small town or else a robust connection and transit corridor to a larger city that you can leech off of. If at the end of the year, you simply don't have enough folks paying taxes, making enough to save a little bit AND spend in an economically healthy manner, your town is gonna starve. Might be fast, might be slow, but if you can't attract some kind of investment, nothing else really matters.
Sure, and that describes the death spiral pretty well. I guess my question (and I genuinely don't know the answer) is to what extent the failure to adapt to the changes is someone's fault. In other words, one of the reasons that immigration is good because it brings in the people who are willing to go through hardship in order to improve their lot. To what extent are these towns' collapse a reflection of the fact that the only people who stay are the ones who are unwilling to change?