Why do we use the term Quick "Bread"?
Cooking terminology is vague and has evolved to suit the avilable ingredients in various places at various times. This means that the categories are not clearly defined.  Here are some examples to indicate the continuum between bread and cake.

There's a whole range of unsweetened soda breads (note: most yeast bread isn't completely sugarless).  Many cornbreads fall into this category (though the one I make has some honey in it).

Teabreads, banana bread etc. are usually baked in a loaf tin and sliced like bread.  They may be buttered; similar loaves are even served with cheese in case you're not confused enough.

But teacakes are bread, in that they're yeast-based.  Not all have much sugar in the dough, though the recipe I've linked does.  Chelsea buns are an unsweetened yeast dough with a sweet filling rolled and baked in.

Brioche is undoubtedly a bread (yeast), but is often sweet.