… it's not for consumers. It's for their customers. Which are video editors.
it's not a consumer product, video editors can utilize multiple streams of video in many usecases. The iMac and the Macbook Air are the consumer products with enough performance for 99% of users.
This generally isn't aimed at consumers; the much cheaper Mac Mini and iMac would be more appropriate there. It's for creative professionals (and to some degree programmers, though I really wish they'd make a similar-sized chip with less silicon budget spent on GPUs and more on CPUs...)
I also don't see how the size of a desktop computer matters, other than as a fashion statement.