1.App Store restriction: App Store no longer provides downloads of old versions of apps. This is because developers usually update applications to fix vulnerabilities, improve functionality or provide a better user experience. Therefore, the app store only provides the latest version of the app for users to download.

2. Compatibility: The old version of the application is no longer compatible with the latest operating system version. In order to ensure the stability and security of applications, developers usually optimize and test the latest operating system version. So the old application can't run normally on the latest operating system.