any wine cellar worth its weight has glass panes which filter uv. That being said it is smart not to store in direct sunlight or next to dishwasher, washing machine/drier etc.
The glass does allow some visibility and if you use wine tags (goes on neck of bottle) you can see what the wine is, window for drinking, etc as I do.
I would imagine it also is for art so to speak. Larger models glass is an option often, but smaller models often go under the counter and hence the glass asks somewhat as a display case. MY under the counter model actually has an area built to display a few choice bottles if you so chose to.