Ask LLM to make a 98/XP styled website and you will discover the reason.

Not sure why they downvoted you because you have a point - icons are not the same as Windows XP's, wallpaper flat color reminds me more of Win 95/98 and the taskbar design has some details that do not match precisely with Windows XP's. I'd also bet it's due to copyright concerns

Because it's obviously vibe coded (look at the source code).