It does seem like while tons of people are happy to use iPads and iPhones, lots of people also have computers that they use for work or hobbies that are not easily boiled down into using somebody’s random app that. Many people have an iPad and iPhone and also and a Win10 PC. I think at least in the business and SW developer sector Apple is losing business with their “lock it down” strategy on their Mac’s.
Besides, while the boilerplate for Hello Triangle is indeed very big, it makes a lot of stuff easier to express on top of it. GL may have a much smaller Hello Triangle, but you have a lot less control over it, way too much stuff happens under the hood. And regardless, if all you want is to animate a web page with fish on an aquarium you really should be using GL instead of Vulkan.