This is purely my opinion but it is a TINY BIT based on conversations I had with clients who were senior accountants at two huge credit banks - the types of folks who actually fund the underwriters.
First of all, Discover doesn't finance all credit cards themselves, they use ABS (see my post) to get investors to fund credit cards. The APR rate offered on a card may be directly tied to the person's risk profile (not just credit score) and their risk profile internally is part of how a bank puts a specific person's specific credit card into an ABS tranch. So at 24.99% you may be in the D class tranch (subprime but not the worst) for example.
At some point in a person's credit life, their risk profile may change enough that a bank sees a profit by including them in a different ABS tranch. Tranches are complex beasts, with individual credit lines sometimes being stuck in one tranch for 5 years but in other cases they may be "sold" to a different tranch to make room for someone else. Computers and AI algorithms calculate this, not humans.
If you're given a lower APR, it's feasible it's because the bank wants to bounce that card from a D tranch to a B tranch (better) for whatever reason. Maybe it's because a bunch of B tranch card holders closed their accounts and investors want returns. Maybe it's because your risk profile is desirable for a different tranch. We will never know, customer service agents will look at you like you're an alien if you bring it up, and even the EO can't help you because the EO doesn't manage the ABS corporation subsidiary!
When you sign up for credit, you are a customer of the credit bank. The credit bank needs funds to finance your credit card, so they assign you to a subsidiary investment bank that markets your profile to investors with a bunch of other creditors. You have absolutely zero relationship with the investment bank so you can't call and ask about it.
But that's my take on APR reductions and why some folks get it, some don't, and some folks get it automatically without asking.
