Obviously it wasn't that people couldn't figure out how to do that. It's that nobody understood that it was an important thing to be able to do. It seems really obvious in retrospect, but it wasn't.
Today, there still are a surprising number of people who create network-accessible persistent objects without making them URL-addressable. Apparently it's still not obvious to everyone that it's an important thing to be able to do.
Rohit Khare's article, "Who Killed Gopher?", helps to make the history a little clearer: http://www.ics.uci.edu/~rohit/IEEE-L7-http-gopher.html
Is remarkably similar to:
Don't get me wrong. The Web is one of the most important developments in the history of computing, or even of mankind.
But like I said, the original article makes the URL out to be some unique, genius invention that came out of nowhere. When in reality it evolved very naturally out of existing network computing practices.
Here's the clue that the article is wrong; when URLs came on the scene everybody who was using the internet at that time understood them intuitively. That's because they were a natural evolution of what was already there.
Of course, that's usually the case with just about anything people say is revolutionary and came out of nowhere. If you look at the actual context that the thing came from, there's a completely logical progression. It only seems like it came out of nowhere to people who weren't there.