Their telemetry data didn't seem to help them figure out how important the start menu is for users. I doubt it's going to help them really do anything else either. They might have the data, but they're not using it.
"Only 3% of users regularly use the start menu." was the justification.
Then they did a bunch of research with eye tracking software to justify the new 'start screen' saying that it was actually better for users who do use the start menu because they were able to locate an item on the full sceeen overlay faster than the traditional start menu.
So of course they figure they can insert ads for their own shit, make it a Bing website search, whatever. People don't want fucking an internet search. They're looking for things on their computer.
You're not supposed to "look" for where something is, you're supposed to know. Just like you're not supposed to look for the X in the top right corner of an application. You know it's there and you know that if you move the mouse into the corner you can click it (which is very infuriating when some UI design decides that the top right corner pixel does not count for pressing the X button). The start menu in the bottom left worked in a similar way.