???
Must be playing a totally differnet Civ IV than you do...
It's definitely happened to me before. I've played games where at the Astro exploring part of the game, I come across empires that have filled their borders so much as to have cities that don't have real food... and other empires that still have half of their continent unfilled.
In the last game I was talking about in general (where I lost to AP cheese), one civ left a space where there was a silk and a fish in the BFC, another civ left a space with an oil and a fish(though to be fair, it couldn't see the oil), and an infantry-equipped civ failed to take over a barb city on its continent circa 1600 AD on marathon that had access to 2 fish and an oil in its waters (and that civ was the first to plastics)!
The worst offender I've ever seen (that I could only prove by opening WB after making an educated guess), was hatshepsut gunning for the pyramids on an emperor game. She had failed to found a single other city, and decided to build pyramids without stone. She eventually lost the bid, and it was like she just gave up on the game. She let the other civs around her take every available expansion spot, even when the mids had failed and she could go settlers again. She was at 1 city in 500 AD when I conquered her one-city, wonder-less, completely backwards empire.