That isn't true though, coupons, boarding passes, and even confidential documents use Eurion marks. It's not everywhere because it isn't worthwhile going through the hassle of getting printers that can print them; while 3D printing OEM parts would be much more valuable.

Who issues Eurion-marked boarding passes?

That strikes me as extremely counterproductive given the actually sensitive part of a BP is an (outside of the US) unsigned, semi-publicly-documented barcode.

When flying with easyJet, we can just print boarding passes using any old printer. As long as the number matches up, no security is required.