davidjharder The vast majority of operations in a file manager is navigation or opening a file or folder, so it makes sense to prioritize that action. It doesn't really change much in the way of file selection, even with double-click you still need to ctrl+left click to select another item, or shift+click to select a range of items, just changes the default behavior for single click on a single item.
You also don't go double-clicking on any aspect of Budgie (or GNOME Shell, where my initial stance of switching to single-click started) to trigger the desired response, whether that is applets (or icons in IconTasklist) in Budgie Panel, desktop entries in Budgie Menu, in Raven, etc., they're all single clicks so makes sense to keep things consistent.