The Tables seem to start off with default column widths which have to be adjusted manually.
First select the columns in the top border ( The gray A B C )
Right Click ( command click or two finger touch on Mac) then in the menu select optimal column width, then OK.
Details that may influence the result.
Cells can have automatic wrapping of text ( format cells → alignment → automatically wrap text ). The optimal column width may wrap words in these cells to make the cell contain multiple rows of text.
Joined cells can also influence the optimal column width.