Everyone knows that the web is huge. Really, really huge. But remember, Google indexes and searches only the public web, not the much larger deep web. Furthermore, it searches only the current web, not the two decades worth of deleted pages. So still huge, but maybe just plain huge.
But the job of libraries is to provide access to the collected, recorded knowledge of mankind produced over the past 5000 years of history. That includes the public web, the deep web, and archived versions of old web sites plus stone tablets, scrolls, books, journals, documents, newspapers, letters and e-mails, maps, microfilm, audio and video (both digital and analog), statistical data sets, the list goes on and on. Despite massive efforts to digitize older materials, most of that stuff isn't online--and most of what is online is locked away in the deep web.
So if what Google searches is huge, then what libraries have to search is best described as super-mega-uber-hyper-huge (a new technical term which I hope catches on)!