Because a little Vi is better than no Vi.

Seriously though, I have used quite a few Vim emulations in several editors and I find them very useful (VsVim, Evil, ViEmu, Vintage...). In fact, I think of this 'embeddability' as one of the major features of Vim. I can use Vim key bindings in Visual Studio, Eclipse, Sublime Text, Emacs... all this very much improves the value proposition of learning Vim.

Rather than being an editor with Vi emulation bolted on, Vico is an attempt to do Vi in Cocoa. Of course it is not Vim, with support for plugins, but for someone who is interested in some of Vi's power in a native Mac UI, it is an interesting proposition. Vico is also a way to learn Vim, commands available in the menu are shown with the Vi commands as shortcuts, rather than Alt-key combos.

I can see however as a paid Mac App Store product, it would have been a tough sell. Most people who seek out an editor in the MAS will likely be looking for something with more form than function. But as an open source app, like Vim, I hope it will see some renewed life.

oh, drop the fundamentalism already.

Because MacVIM doesn't behave like a native Mac app.