> Where did it all go wrong?

Just landscape changed significantly comparing to 2010.

Before you didn't have current smartphones and tablets. On desktop you could just support windows only (today probably have to macOS as well). On browser you didn't have to support Safari. You didn't have to worry much about screen DPI, aspect ratio, landscape vs portrait, small screen sizes. Your layout didn't have to be adaptive. There was not much demand for SPA. Back then there was much less people worldwide with access to internet.