Because "you'll take your 4:3 480i and love it!" isn't going to go over well with anyone, nor can you actually distribute that particular format anymore these days (Amazon's lowest quality is probably 562p -or whatever the correct number is- or so). The technology itself also no longer exists in any working practice, so you'd never get that.
Also, Darkplace is far too experimental for what Amazon is pushing for at this time. The BBC can do experimental due to not being a public business.
The technology exists to make anything look like anything so that's not an excuse.