This is a conscious design decision and the dropdown menus follow the convention followed by the Bootstrap CSS framework.
As you can see here, the dropdown opens onclick and the parent node is always “#”. That allows touch screen users (such as those on tablets and mobile phones) to utilize the menu by tapping on the parent menu node (since there is no “hover” on touch screens).
Also, if the main node takes the user away from the page on click, then the user may not be able to see the dropdown options.