There is just that scratching-on-the-board feel when I screw the metal cap back onto the glass shaker. Also, it will break if I happen to drop it.

What is behind the glass factor?

Lets say, why not plastic? It's cheaper to make and doesn't break. Does it have to do with taste? I don't notice a difference in taste between salt stored in glass and plastic.

Glass is used as it is non-reactive to salt. The same applies for most plastics.

Iron based metals for the most part are reactive so that is why they aren't used.

We have a wooden salt shaker to match our wooden pepper grinder. You just have to look around for them. More garage sales than department stores, I'd say.

I don't notice a difference in taste between salt stored in glass and plastic.

Go into any McD's and its in plastic so no issue there w glass vs plastic. I imagine people like the weight of glass better, feels less cheap than plastic.

We have ceramics that you fill from the bottom and stoppered with a flex plastic plug.