For clarification, you can recursively sync everything, expanding all folders and showing all files as placeholders using a right-click action. As @Ethan stated, there are good reasons why we don’t want to do this by default, but users have the option to do it, if they want to.
Right-click->Sync on the desired folder
Move the slider to “Nothing” and check the “Include subfolders” checkbox
“Save and apply to new files and folders” is a Premium feature that will set a rule on the selected folder enforcing these settings on any remotely added content, as well