When it comes to credit cards and their limits, there are two basic extremes out there, there are those that barely qualify for a credit card and thereby they are stuck with limits of a mere $300-$500, or enough to put an airline ticket on a credit card, or get a hotel room for a few days, or have available credit as an emergency spending backup and not much more; then there are those that have credit limits of $25,000 or $40,000 or even $100,000 or possibly even more for certain special credit cards that are issued without a preset credit limit. Clearly, there is a wealth of difference between the two credit extremes, yet we know this truism, that banks are noted for extending bank loans typically to people that really don't need loans, so too this is true for those that are issued insanely high credit card limits, because the banks would not issue such high amounts, unless they had clear documented evidence that the person receiving such high credit card limits had the capacity for paying such.
One important thing to remember about credit cards is that the credit being loaned to the consumer is unsecured against any of that consumer's assets, which means, should things go terribly wrong for the consumer, and ultimately for the bank issuing such card, that in order to recoup their money, that bank will have to take to take active measures to recover those funds, through such possible means as phone calls, collections, and/or court. All of those actions will cost the banks money, resources, and time, with little hope of collecting even close to 100% of the debt, making one wonder whether it's worth the risk of issuing such high credit limits without some sort of asset protection in the first place.
The banks do have some protection for the amount of the credit default that they are subject to in the sense that even though they may issue a credit card to you for $40,000, there is often an implied understanding that you as a consumer, will never actually be allowed to "max out" the card to $40,000. Whereas in most credit card transactions the purchase automatically goes through, in situations when your credit card is being used perhaps more than three times in one day, and/or for amounts that you typically don't charge, and/or in a location of a city that past history shows you are seldom or never at, the credit card spigot will completely y dry out, pending a phone call to that lender, and a conversation ascertaining exactly what you are up to. So, for example, today you are buying that super-expensive piece of jewelry and the bill is $25,000, in all likelihood, no matter how pristine your credit, there will probably be a conversation with your lender before the charge is authorizedand goes through.
This leads to the point that a significant part of the reason why high credit card limits are issued, is that the lender wants you to use their card, hoping that you will purchase things that you might not normally purchase precisely because of that credit card, and by doing so your credit card bank can make their merchant's fee on sales that would have never transpired without the higher credit limit. The bottom line is that higher credit card limits are essentially given to people that have the capacity to pay off those limits, to encourage them to spend more than they might.