There's a lot of things that people do that aren't for practical reasons. That's why all our homes aren't just concrete cubes. Somebody must have decided that this looks cool and futuristic.

Strictly from practical reasons, I suppose it's marginally easier and faster to identify a free stall. Whether that is worth the extra cost is subjective.

Also, the default state for this glass is frosted. In case of a failure it all becomes frosted.