I can't speak for the developer, but as a TextMate user who has dabbled in vim/emacs over the years, my take on this is it's about "polish". Like MacVim is line-based, and when you scroll or resize the window, it moves in "chunks" of one line instead of whatever pixel-precise position you drag the mouse to. And using mac-standard "command" key shortcuts instead of different modes (for vim) or control-key ones (emacs). [Yes I know that can all be customized in vim/emacs, just talking about out-of-the-box]. Also the "project pane" in TextMate is very mac-like, whereas in Vim you have NerdTree which is totally text-based (in the sense that it's like "curses" graphics-via-ascii-characters as opposed to icons and lines and non-monospaced-fonts), or emacs which gives you the buffer list at the bottom (if I recall). And I was never able to figure out how to get a project-wide search going in Vim. Also, the window chrome, which I guess you could classify as "shiny", but little things like that do appeal to a lot of people -- same reason people like the shiny and smooth macbook hardware vs. more boxy windows laptops.
Not saying this is objectively better, just trying to answer your question. And of course I understand there are tradeoffs between polish versus flexibility. For example, the Mac editor Coda is super-duper shiny and maclike, but it's way too inflexible for my personal tastes, so I wouldn't use that. But something like TextMate seems to hit the sweet spot for me and a lot of other people.