Theoretically, credit should be used for one thing: to make more money. (not less) However, instead of using it to buy or construct a machine to triple what you can produce in an hour, the average person is using it to delay having to work that hour at all, in exchange for having to work an hour and six minutes sometime later. At some point, you run out of hours available and the house of cards collapses. i.e., credi…
I tried using one of these offering a 0% intro APR to finance an upgrade to the boat I eventually moved into (saving me 10s of thousands in rent.) They wouldn't let me do it despite having an upper 700s credit score. It's not clear to me how they pick people to lend to.
There's also a lot of reasons one might be rejected for a credit line that have nothing to do with credit score. Some lenders have specific policies in addition to credit score, like Chase's 5/24 rule. Some are also just looking for "relationships" and won't offer you their best products unless you have a bank account with them, etc.