WRT what hulitu refers to (as i understand it), it isn't Tcl/Tk that makes the GUIs more usable, it is more that the modern trends that largely came out of small touch screens and often use flat(ish) themes with a lot of padding and unused screen real estate that make desktop applications less usable.

Tcl/Tk just makes it harder (though not impossible) to make such GUIs because its defaults were made before those trends, but it isn't unique to it - the same applies, e.g., to applications made with Qt Widgets. Note that here i do not refer to how easy it is to make the GUI, just on how usable applications are from a desktop user's perspective when using the default look and feel.

This particular problem is largely a matter of trends - some libraries/technologies make it easy to follow those trends, others harder, however the root issue isn't so much the libraries/technologies in question but the trends themselves.