The Missing Installers
macOS and the Safari browser try to help you manage your storage space by automatically handling downloaded files. In Safari, there is an obscure setting designed to keep your Downloads folder from bloating over time. If enabled, Safari will automatically delete files from your Downloads folder upon successful completion, or after a specific time limit. While this might be helpful for temporary PDF menus or single-use images, it is disastrous if you use your Downloads folder as a staging area for large applications (.dmg files) or zip archives, as macOS will silently purge these massive files before you have a chance to back them up or install them.
Preserving Your Downloads
To ensure your files stay exactly where you saved them and stop macOS from automatically emptying your Downloads folder via Safari, you must alter the browser’s file management preferences.
Open the Safari browser. In the top menu bar, click on Safari and select Settings (or Preferences in older versions). Ensure you are on the General tab (the first icon). Look down the list of options until you find the dropdown menu labeled Remove download list items. By default, this is often set to “After one day” or “Upon successful download.” Click this dropdown menu and change the selection to Manually. This stops Safari from automatically clearing its internal download history. However, to ensure the files themselves are never touched, you must also uncheck the box immediately below it labeled Open “safe” files after downloading. If Safari auto-opens a zip file, it will often automatically delete the original `.zip` archive to save space. Unchecking this box forces Safari to leave the raw file intact in your Downloads folder forever.