Well, that harkens back to when generic brands were big in the 1970s, they were intentionally extremely plain to get across the point that it's no-frills.

http://historysdumpster.blogspot.com/2012/08/generic-product...

"The idea behind them was by eliminating the cost for logos, descriptive copy, and photos/illustrations on the packaging, the savings could be passed on to consumers. Even though much of these were stock images anyway and in reality bore little extra cost in the actual manufacturing process."

I think it's the same psychology at work.