Because this is for Opera Presto. You can enable sync for Opera Blink on opera:flags but it doesn't sync bookmarks yet.
Run Opera with the parameter "--presto-small-prefs-dir=ROAMING_PROFILE_DIR" without the quotes and with the correct path to your Opera Presto (Opera 12.xx and older) profile.
Note: This will reset your Opera 20 profile and you will loose all your settings/info