My impression is that it has primarily to do with attention.
When people perceive something, they need a certain amount of mental stimulation to feel good. If there are too many details competing for their attention, or one thing sends too strong a stimulus (such as a very saturated color), they are overwhelmed. When we are talking about seeing design (in typography or something else), we experience such an object as cluttered or garish. On the other hand, if something does not have enough details or is too subdued, we perceive it as boring. A positive emotional reaction ("like") needs a Goldilocks middle.
But there is a difference in stimulation between typographers and non-typographers when looking at fonts. In the process of learning to be a typographer, a person learns to notice the details of font and layout and to attend to them. For the non-designer, it is as hard to notice the difference between Garamond and Caslon as it is for the designer to notice the difference between balls of ciabatta and pretzel dough (unless the designer is also a baker). This means that the amount of stimulation provided by a font is very different to the designer and non-designer. Where the designer sees leads, slants and m-widths, the non-designer sees text. A font which falls into the "perfectly balanced beauty" category for a designer falls into the understimulating "I see nothing interesting" category for the non designer.
So, a non-designer wants to create a document at her home computer (which came with MS Word). And she also doesn't want it to look like all the memos and reports which swamp her at work. She writes the text and looks at the list of fonts. They all look similar to her. The ones which catch her attention are the distinctive ones: the blackletters, Comic Sans, Papyrus. When she tries them out, her text looks different - and to her eye, this difference is pleasant and refreshing (aside from the blacklettering, which she probably finds unreadable, and maybe also associates with weird antiquated books). Looking at it engages her in a way which is not there when she looks at the same text in Arial. So, she leaves it at Comic sans, and may even add some bright color to catch the attention.