I've seen unity in action, and I must say I'm impressed. It's just what I was looking for a few years ago. The universal top-bar, the ease of sorting your opened applications, the look, the feel, everythings nice and nifty. The only thing I don't like is the focus on mouse-use.
So it's everything I wanted a few years ago. In the mean time though, I've learned a lot about linux, other WM's and DE's and learned how to operate them. It's because of that that I've ended up with crunchbang: light and nimble and still does everything I want. I'm a big dmenu user and I've made scripts for everything I wanted 'automized'.
I also realize that not everyone wants to learn how to use a computer (and that's a damn shame, but not something I want to talk about now), they just want to email, use facebook/twitter or browse the web. For them, the computer is a completely different thing than it is for me. And that's fine.
My dad, for example, knows how to do 5 things: 'using' word, using IE/firefox, using outlook, scanning a document, and using MSN. Anything else is voodoo to him, and he hasn't the slightest interest in learning about it. And that's fine.
One of my friends, a windows user, wanted to learn linux. Knowing how he uses a computer, I managed to talk him out of it, since while he said he wanted to learn linux, he really doesn't. He has remembered my shiny compiz-all-the-way-setup from a year or two ago, and he just wants something shiny to show off with. He's not a technical user, he hates to have to figure things out, and he uses his computer mainly for gaming. I don't want to be the one introducing him to linux, I simple haven't the time to spare to teach him everything. So he still uses windows, and is planning to buy a macbook pro in a few months. And that's fine.
Different people have different ways of using a computer. What's a must-have feature for one person is a showstopper for someone else.
I personally think it's great what ubuntu is trying to do. I've used ubuntu when I first started with linux and loved how they took you by the hand. A few years later, I'm annoyed by that same fact, turned my back at ubuntu and am having great fun with crunchbang/debian/my own hodgepodge of scripts and helpers.
There's no one-size-fits-all in OS-land. There's just different ways of doing things. Therefore I don't believe you can say 'Why copy an awful Desktop Environment?', while you actually seem to mean 'Why copy a Desktop Environment that I don't like?'.
I personally see people using facebook and twitter, and having perfectly valid reasons for doing so. I also see people avoiding google, also for perfectly logical reasons.
I don't use facebook/twitter and think they're evil, and I do use google/gmail (while at the same knowing they're also evel. ish.).
Difference is the keyword.
laptop: asus zenbook UX31 [debian wheezy, kernel 3.3.0-rc7-custom]
tablet: acer iconia a500 [honeycomb]
home: C2D E8500, 4GB RAM, 74GB Raptor HDD + 2.5TB in various HDD [debian squeeze, liquorix kernel]