Mastering Perl/Tk, p. 47, says:

If you use -sticky with your widgets and then resize the window, you'll notice that the widgets don't resize as you would expect. This is because resizing of the cells and the widgets in them is taken car of with the gridColumnconfigure and gridRowconfigure methods...

Further reading suggests applying a weight of 1 to each row and column. That will allow each to expand. A row/ column with a weight of 0 takes only as much space as it needs; a weight of 2 would take twice as much space as a weight of 1 (so some can be greedier than others).

yours,
Michael