Maybe you're only using well-designed sites? Try making a booking with a Chinese airline and you'll quickly wish for an assistant to delegate it all to.
funny you say that, I was literally just booking a flight with air china yesterday and the UX was 10x better than the average wizzair/ryanair experience - a clear, readable UI (with a great table comparison of prices +-3 days from the selected dates), no ads, no random services getting pushed in your face, no booking tabs automatically opening in the background
Huh. Last time I tried with them (about a year ago), and more recently trying with China Eastern, I couldn't even get it to show me a flight that I knew was flying on a given day (just at a slightly higher price than the one it would show me).