I've found a few major reasons for the failure apps. The the two most common ones appear to be changes in the operating system (iOS/Android) that make it fail (crashes, etc) and changes made to service provider protocols that make communication with their servers fail. If the app maker has stopped providing updates or cannot provide updates due to lack of OS, hardware or service provider support then it's the end of the line. There isn't a lot of incentive to support 10 year old devices for the original device and component makers. They are in the business of selling new hardware so it is more profitable not to. Sometimes it's nearly impossible for developers to update apps due to lack of resources, such as support for development tools from the hardware makers. Windows support usually ends after 5 to 10 years. Newer Apple (iPhone 6) hardware loses support after 7 years. The best for Android seems to be 5 years. That's for flagship devices from major brands. It's worse for other products. I've seen generic or bargain brands that receive no support at all, even when new.This means that there is no guarantee an app will continue to run on older hardware, there is little incentive for developers to make older apps work, there is no reasoning behind it...
It's not just PC's, phones and tablets that this affects. I have an internet streaming radio that has lost most of its ability to stream music services. The last service that stopped working stated that the device app is no longer supported. I'm left with half a one year subscription that no longer works. Their support person was very helpful in providing a list of other devices that are supported but they were all unsuitable due to lack of functionality. Smart TV apps sometimes stop working after 3 or 4 years as well.