In a world of internet before everything went viral, this story was just 'crazy enough' to essentially go viral. The concept of a page being worth a million dollars both in a literal and theoretical sense made this quite a popular link to share in the initial phase (when the site was empty apart from a couple of adverts).
This then drove a viral / media engine (including television / radio and word of mouth) which suddenly actually made the pixels on the page worth something!
Companies now flocked to get adverts on the site which was getting a large number of genuine traffic / media attention and thus the media cycle continued (as it was now a profitable, extremely successful site) - this in turn finished when the page was full and months later everyone lost interest.
Unfortunately, I think many of the copy cat sites didn't understand why this was successful in the first place. It was a clever new idea, which was likely to get press attention for being so 'unique' / 'clever' - the copy cats were unlikely to ever get the same 'viral' effect, so were never going to become successful like the original site.
If I remember correctly, even the founder himself tried to spin off a second site based on the same concept with limited success - mainly because people had seen it before.