But green isn't the equivalent to goofy conic sans, it's just a color. People in Europe use WhatsApp and it's green.

The problem is that money based status competition is so rampant in America and this is merely an effect of it.

I understand, but that is a different discussion. "Alice doesn't want to appear poor to Bob" != "a degraded experience for Bob". If Microsoft had displayed emails in magenta Comic Sans they would have been harder to read, and thus a worse experience for the recipient, manipulative but still not emotionally manipulative - compare, say you install Linux on your former Windows PC and Microsoft change the boot loader to a war photo of a crying child being torn from her crying parents by an enemy solider and the text "I'll miss you so much".