What if you're halfway down the page but you want to click to another page on the site? How else are you to do that unless the nav menu is on the screen all the time???
Sticky headers are stupid and annoying. Easily the worst UX pattern in the last decade. I bet no one has even tested to see whether they even increase "engagement".
how about something less sinister like not designed for mobile first, and it looks just fine on a desktop with plenty of pixels to be used? like everything else in the world, a decent idea implemented badly makes the idea look bad. also, opinions are like noses. everyone has one and they all smell.
