An app crashes when it reaches a state it cannot recover from. That state is usually caused by something the app reads at start-up or during use, such as corrupted local data, a missing permission, or not enough memory to finish an operation.
Local data is the most common trigger. Settings, caches and downloaded content can become inconsistent after an update or an interrupted save. The app tries to read the damaged file and shuts down instead.
Memory pressure produces a different pattern. The app works fine when the device is fresh but crashes after other apps have been opened, because there is no longer enough free memory to complete a task.
Compatibility issues appear when the app expects a service or feature the device no longer has. This is common on older devices after a major operating system or app update.