It wasn't a rocket science amazing idea in 1989. It was a pretty obvious thing anyone in the space could see would be interesting to try -- hypertext already existed. The internet was just taking off. The idea that you could host pages that hyperlinked to each other on the internet was totally obvious and if you'd explained it to anyone active in the internet at the time (obviously not that many of those people), they'd have nodded. I should add that almost nobody had a computer with a graphics display in 1989 (I did, at work) so that further constrains the set of folk to whom the idea would make sense. The fact that everyone now has many 64-bit computers with extremely high resolution displays is probably the more surprising thing to 1989-dude.