It's almost like people do not remember the mid-2000's where the New York times had the dictionary popups on their website. The worst user-interface that ever existed - double clicking (or highlighting? I don't remember) would display a modal popup with the word definition. This happened on every word, so oftentimes they would popup definitions for 'for', 'and', etc. It was highly intrusive (the NY Times removed the behavior after widespread consternation, turned it into a small '?' behavior).

Maybe if everyone expects that behavior all of the time, it would be worthwhile, and people could get used to it. As it stood on a single website, it was not very valuable.

If you are curious, here is an article from 2011 about the types of words that were looked up using the service: http://www.niemanlab.org/2011/07/nytimes-coms-most-looked-up...