Because you need to remove that same piece of code from the
views.php (within the same folder) before you move it inside your
id="btn_save_quote"). IDs must be unique by definition.
I also agree the "save" button's position is not convenient on top-right. My "options/save" buttons are floating and following user's scroll on top-right of the screen thanks to Bootstrap's "Affix/ScrollSpy" properties, but I like it your way as well, right next to "add product" button.