You are absolutely right, and personally, I'm a huge fan of these tiny niche products that do one thing really well. However, ask yourself this: is the next Apple applying (or going to apply) to YC? My guess is probably not.
Or if the next Apple did, would YC know it’s the next Apple? I’m sure there are companies rejected by YC due to ignorance of the business line or the reverse, ego blinding the reviewers.