Native American Dollars Metal Content

Now as to why they did that?
So they won't be mistaken for quarters like the SBA (Susan B. Anthony) was back in the day.

Not going to pretend I'm an expert, but from a metals manufacturing perspective, I think that composition is likely considered somewhat basic. I don't think the mint officials (regular folks like you and me that just happen to be working for the government) know much about exact metal compositions and what they'll provide to the end product. Big metal manufacturers likely presented various proposals for the contract with different metal compositions that had tradeoffs in terms of longevity, tensile strength, impact strength, visual appearance, etc. Within the metals manufacturing industry, I expect there are countless combinations that have already been tested ad infimum. Again...not an expert...so happy to be corrected if someone else knows the real story.

The problem was they needed to have the same size and weight as the SBA, AND the same electromagnetic signatur, and the distinctive golden color. They could have gotten the color by just dropping the nickel but then the signature would have been wrong. So they leave some of the nickel in, but too much and you lose the color. So they basically wound up tweaking different alloys until they got something that worked. If they hadn't made the SBA then they could probably have just used a brass alloy that would have worked fine. But instead they had to get it right so vending machine could accept either type of coin.

This is why after over ten years they haven't been able to come up with a replacement alloy for the 5 cent piece. Everything either costs more, has the wrong weight, is magnetic, or the wrong signature and they can't co-circulate with the existing coins.

Thank you, Conder101. That really helped a lot!