This may be a few years too late, but just in case anyone else now or in the future has the same question, I'll give it a go...
First off, the term AI is a bit of a misnomer--it's a computer. The computer players don't learn or adapt in any sort of machine learning way. This may be a slight oversimplification, but it's basically just a long series of IF/THEN statements that determine their choices. Difficulty does nothing more than give the computer players buffs to make competing with them harder.
Now to actually answer the question, it probably just boils down to start location. The players that are beating you to wonders very early on likely had a good start location. For example, take a Grassland Hills tile with Woods and Spices. The BASE yield for that will be 4 Food and 2 Production, let alone any future improvements. Now if you had a couple other tiles nearby like a Grassland Hill with Rainforest and a Plains Hill with Woods, you're looking at just 3 tiles with some serious Food & Production yields. This will cause the city to grow quickly, then work more tiles that not only grow quickly, but also have high production. Start location is everything when it comes to Civ. It's important to settle in places during the early game that you can get high yields without having to train builders to improve the tiles, so that when you do finally train builders, you make those tiles even better. Avoid featureless tiles; look for Woods, Rainforests, and Marshes. People can turn their nose up at this all they want, but I literally restart every game until I get a start location I'm happy with. It doesn't have to have a Natural Wonder nearby or anything like that (though that would be nice) but as long as I have 3-4 tiles with 5+ total yields within a 2-tile radius of my desired city location, I'm happy. Ideally you'll have 1 or 2 Luxuries and maybe a Bonus Resource nearby to help with that, and potential for Strategic Resources as well (they're pretty easy to predict when you know what to look for).
Hope that helps!