I am continually astonished at the level of credit card debt many people carry, considering the usurious interest rates most cards charge. According to a few googled sources, the average household in the US now carries nearly ten thousand dollars of CC debt, and the average family pays about $1200 a year just in credit card interest, with an average rate of 18.9 percent! Many of the cards that tout low rates seem to be designed to get people mired in debt, and then raise the rates after a few months.
My guess is that especially after the bankruptcy laws have been modified in favor of credit card issuers, it pays them to issue pre-approved cards, in the hope that people will run up enormous, high interest debt which cannot be erased.
One advantage for the would-be debtor is that if one already has a balance on a high interest card, it might be worthwile to pay it off with a lower interest card to lower the load. But this works only if the lower interest lasts long enough to allow the debt to be paid down at the lower rate. Unfortunately, I suspect few people succeed in this, instead running up additional new debt on the new cards, missing the opportunity to pay down the debt at the introductory rates. When you're in a hole, you need a rope, not another shovel.
And of course a credit card, pre-approved or not, is an advantage to any consumer who never carries a balance. Especially now, with internet purchasing, it's a necessity, and if you do pay off 100% every month, you benefit from the float, collecting at least a tiny bit of interest on your money during the month, while paying none out. I've had a visa card since 1972, and have probably paid out a total of about 50 bucks in interest in that time, owing to accidentally missed payments during moves, long trips, etc. It's a very handy thing to have if you remember not to spend money you don't already have.
But non-debtor consumers are in the minority I think. You can be sure that if credit card companies issue preapproved cards, they are benefiting from it, and since debt is the driving force for the multi-billion dollar CC industry, that's where you'll find the motivation.
Edit to add: here's an interesting web site with some statistics and observations. Note that along with everything else, credit cards tend to increase the average size of a transaction. People tend not to count their money when they're not physically counting their money.
http://www.bankrate.com/brm/news/debt/debtguide2004/debt-trivia1.asp