There is a tension between elements of a GUI that is difficult to resolve by just resizing.
Graphs can mostly be resized arbitrarily as long as the aspect ratio is preserved. There is a lower limit below which not all of the detail can be discerned, but humans are pretty good at understanding that "space was limited" and mostly be forgiving as long as the general trend is still visible.
Text, however, gets unreadable below a point, and "looks wrong" if it is too large for the situation.
The proportions that are accepted for graphs are not the same proportions that are accepted for text.
Meanwhile, the sizes that are accepted for some of the user interface elements such as scroll bars sit within a narrow physical range, and do not scale well.
The result of all of this is that mostly you have to let the UI elements sit around a certain physical size without scaling, and that you probably want to constrain how large text will get, whereas graphs can scale up.
In particular, you probably want to re-flow text when you change the proportions of the container rather than scale it up proportionally. And if you define the size of a particular section of a ui as being "just large enough to comfortably fit this text" then you end up moving pieces of the interface around as you resize, and you start to have to develop rules such as "This element is variable in size to fit the current font size representation of this string, and this other element should be just to the right of it and the same height". You start to develop a "layout" instead of fixed positions.
Layouts are beyond the scope of GUIDE. App Designer starts to provide some layout tools.