It seems to me that anyone who ranks in the top 10 of any of these worlds clearly spends thousands of dollars to play, so I'm not sure why a player with money would bother to have a 100 accounts just to gain rank?
You're right that they do spend thousands. Tens of thousands, even. Inno promotes that by ensuring that the best items cost diamonds, and that everything steadily gets more and more expensive in terms of space, time, and gold/goods/whatever required. Just stating the obvious for anyone who hasn't figured that out yet.
However, there are players who will do anything to be at the top in ranking. If they can't earn it or buy it, they'll steal it. They typically have 8-10 or more alternate accounts (some even have full Fellowships of alts) and they set them up as "farm" cities, where they usually concentrate on producing two things... troops and usually one type of goods. Most you can tell right away are not cities that grew organically through game play. All magical buildings, all premium culture, and row upon row of armories and factories to maximize output per square.
By concentrating on pushing the goods they produce back and forth (transferring members from one FS to another temporarily, or carefully ensuring that members of one FS are conveniently neighbors of members of the other) they're able to exploit tournament and map expansion by catering for maximum KP, as well as getting 10 chests every tournament. They push the resulting KP to their main accounts, driving their Ancient Wonders FAR beyond what you could reasonably expect a player with a single account to achieve. They use diamonds to end the upgrades quickly and hide the evidence, but it's there for anyone who spends any time at all looking and is good at detecting patterns.
Obviously that's not fair to people who don't want to buy diamonds and don't want to resort to cheating, but still want to play the game and succeed. If you've got a cheating player whose ALTERNATE accounts are regularly placing in the top 20 in tournament and soaking up all the ranking points even though their game scores are only in the 10-30k range, how is that fair to someone who may have put in the work to achieve a legitimate game score of 200k+ but can't even hope to score that high in tournament because they don't have the massive amounts of goods to cater?
When tournament started on Sinya Arda, 2,000 points was a good score and 3,000 was stupendous. Now 3,000 points won't even get you in the top 50, and there are players who regularly post scores of 6,000-7,000 points or more... from accounts that couldn't possibly produce that level of goods or troops to cater or fight. I've even seen one break 10,000 points recently. Explain to me how you get 10,000 points in tournament with the resources of a single account and with the troops you're able to amass since the the last tournament only a few days previous. There is only one explanation for that, and it's not diamonds. Not directly, anyway.
Everyone should know by now that online games aren't really free, and that to get the best of whatever, you're going to have to resort to in-game purchases. That's the business model, after all. But if you're going to have rules that prohibit using multiple accounts to push another account up in ranking, then stick to those rules and don't just ignore them or change them because it benefits you financially. Everyone should be playing on a level playing field with known rules, and if they choose to spend money to advance, they have that choice. Players shouldn't have to choose to cheat to advance, or compete against those that do.