I think it comes down to the degrading quality problem for brands and products.

One thing I have in mind was suggested by another user:

To combat brands changing over time as they often do, graphing the rating over time may let you see when/where the brand went from quality to cashing in on the recognition. I could see such a feature eventually evolving into more, like allowing people to highlight major points on the timeline (like an acquisition or change in manufacturing location) or letting you filter reviews to a certain period.

But that's quite a big feature, something for the future :)