Because folks are looking at their screen rather than looking at the external components. Which is why black bezels are so nice. Hello?
Hello! Any chance you have a car? Or a bike? Or a painted/sided/stuccoed/brick house with an exterior color? Or clothes? You're not looking at any of that when you're
using any of those things either...but if you have any of those things—I'd confidently bet you care(d) about the(ir) external color, regardless.
You like black bezels? Great. I like them too. I'm using a black-bezeled screen now.
I don't consider white bezels bad, though—even when doing video/photo/design work. Apple has done it before and it was fine—on iMacs, MacBooks, iPhones and Cinema Displays. A grey bezel was on their laptops for years, and people weren't so worked up about it then, and the usability wasn't such a disaster that they didn't sell millions of machines over years and years, coinciding with the company's return to popularity and prominence. White bezels are a design
choice made by people with more combined education, training and experience than probably every person on this forum put together, not a lack of talent or skill or a display of incompetence. Does that mean that everything that Apple puts out is beyond reproach? Of course not.
...but it
does mean that there were thousands of inputs/factors/constraints that went into the choice that the armchair designers here have zero insight into, so to make such strong proclamations about "failure" are disingenuous.
I appreciate that they zag-ed when everyone—especially the Chicken Littles who claim that most everything that comes out of Apple is some design failure—expected them to zig. Especially knowing that that all-in-one Dell and thousands of other options are out coated in black and silver and nothing else for people who like their possessions boring and unremarkable.
I don't always agree with their choices, but a big part of why I
like Apple is that their design choices are strongly
opinionated. To me, putting up with a misstep here and there is
infinitely preferable to the company falling into the crowdsourced trap that Henry Ford warned about:
“If I had asked people what they wanted, they would have said
faster horses.”