Two things from my memory. 1. They hit some bad PR when they pushed a badly broken release in a point update. Turned out that their testing was not robust, while Lodash's is excellent, which further hurt them (this is when I first remember hearing about Lodash) 2. Lodash adapted better to the module landscape, especially by splitting all of their functions into separate packages.
It's great, but there are better alternatives. Ramda[0] is great, auto-curries everything and has an api similar to Clojures, which is really great. Lodash[1] is a fork of Underscore, with some OOP-isms replaced for FP-isms, which I and many others prefer.
