Regarding hardware quality: "...why there's no PC manufacturers that would have the same overall quality of the hardware." In my experience, business ThinkPads beat MacBooks by a mile for working (e.g. programming). I am surprised to see so many coders use MacBooks. Thinkpads have better ergonomics, are more robust and better performance/configurable hardware (e.g. RAM).
1) MacBooks are pleasing to the eye. ThinkPads are well-designed functionally but ugly. Aesthetics don't matter to everyone, but to those for whom they do matter, they are not a frivolous concern. Working in an elegant environment (including hardware) can have a positive effect on one's state of mind.
2) A lot of people are interested in developing iOS apps. This is much easier on a Mac.
3) MacBooks are status items like designer clothing and may make people feel more attractive / successful. Obviously this is not universal but neither do I think it's a negligible effect.