Because the savings would be less than peanuts in the grand scheme of things that the government spends money on.

Because the Left would be galvanized by a million blog posts and academic papers (basically the same thing these days), arguing that it's racist because people of color are more likely to be underbanked and use cash. Yes I realize that's nonsense, but it wouldn't matter.

Because the Right would probably be galvanized too, by complaints that the government was meddling too much in the familiar and somehow ripping people off. Yes I realize that's nonsense, but it wouldn't matter.

It's so hard to make anything happen in U.S. politics today... eliminating pennies, nickels, and dimes wouldn't even make my Top-10,000 list of priorities.