Layouts and Tables are two different things even though they often have exactly the same names.
FileMaker does not necessarily add a new field to a layout at the time you define it. Often, you have to use the field tool to add it to the layout or, in table view, use the modify button to add it to the view.
There's a preference setting in Edit | Preferences that controls this. It only adds a field to the current layout so if you are on a layout for Table A and use manage database to add fields to table B, they won't show on the layout for Table B even if this option is selected.
Given that detail and the fact that you can't control where the fields are added on the current layout, I find it easier to leave that option disabled and then use the layout tools to add fields where and when i want them.
Thanks. Your answer gave me the solution to my problem