So why do they keep offering me incentives to use their product? Is it the hope that one day, after 20 years, I'll finally overspend and they'll get to collect some interest from me?
This isn't to say that they don't still consider you a low value user, since you're not providing them with much in terms of direct revenue. Yes, finance companies love it when you hand money directly to them and won't mind if you forget to make a payment after 20 years and and up paying interest.
You may be unlikely to overspend after 20 years because you are financially literate, but if you're paying off your credit card every month, you and I are very much outliers on the bell curve of net worth in the US. If you have an engineer job you almost certainly are an outlier. We aren't the target audience of these ads. There are a lot of people in the middle of the curve who mostly pay off their credit card every month but might slip once or twice, and they want to optimize that probability of slipping.
You've paid off every month on time for 20 years, and they get 1% of that. For basically running some servers and balancing payments.
That's big money - debit cards do the same thing for what, 25 cents a payment? So once the credit card hits about $9 it's all gravy.