Sinofsky kept talking about how many devs were making apps in JavaScript and how they would just be at home in Win8. This was before React, ES5 (no native classes! or promises!), etc- jQuery was still very popular and SPAs were extremely rare. He completely overlooked how dependent many of these devs were on their servers- Python, Ruby, PHP, etc.
They thought after V8 the performance was going keep improving and reach native speeds, they didn’t understand that the major performance wins were all upfront and it would hit a wall.