From being a nature photographer, I have a guess about why Apple makes the glossy screens available, and makes them standard: Most people like eye candy. Most people like things that are shiny. People prefer lurid, unrealistically oversaturated colors. People prefer greatly exaggerated contrast.
In the days when film photography was popular, film manufacturers did lots of market research, and came to realize that most people wanted films with the same characteristics as we now see with the glossy screens. Hypersaturated, hypercontrasty films, such as Fuji Velvia, greatly outsold realistic films. The same was also true with photographic papers – and, by the way, besides the fact that high contrast papers and hypersaturated papers sold better, glossy papers also sold better than matte papers, and glossy prints sell better than matte prints.
Hypersaturated, hypercontrasty pictures sell better than realistic ones (and better than the same picture with less saturation and contrast). It would be hard for most nature photographers to make a living, if they didn't hypersaturate the colors in their photos. It's almost, but not quite a requirement of the business.
So, I'm guessing that people react to hypersaturated, hyper-contrasty, super-shiny screens in the same way. I don't think that is so much a result of marketing, as it is simply a trait of human nature that the majority share. If so, marketing the glossy screens as standard is probably in their best business interests, even if it is a questionable decision from a functional viewpoint.
By the way, I'm writing this as someone who prefers matte/"anti-glare" screens. I find the reflections on glossy screens very problematic, and find the blocked up dark tones problematic, for my work with these computers.