Because I've been using it for months now and the text is perfectly legible. Some of the very early beta had too much transparency but they've drastically tightened it up and now it's not even noticeable. Safari was probably the most noticeable fix they applied—the URL/tab bar is near fully opaque now. They're way more aggressive on turning up the opacity on backgrounds with the same text color. The readability issues are being addressed and is a fixable issue rather than a condemnation of the whole design system. I still think it's a gimmick but it's firmly in the visual preference territory instead of measurably worse.