What my motivation is finding out why most other banks give me a much higher credit limit vs the medium limit that Amex gives to me?

If someone spends $40k a year on Surpass to get Diamond, how much is that worth to Amex? Is it worth $100, $500, $5,000? I have no idea but someone here must know?

I could care less if Amex comes after me if and when I drop them but my whole issue is this low credit limit and how it affects my spending pattern.