Software runs on top of other software. An app depends on your operating system, which depends on drivers, which depend on hardware. When one layer moves and another does not, things break in ways that look random.
Most crashes people report have already been fixed. The update is sitting there, waiting, blocked by low storage, a paused download, or a device that never gets restarted.
Security is the other half. The majority of successful attacks target flaws that were patched months earlier on devices that never installed the patch.