There are several things. First, the fragmentation of having several of any thing you named doesn't spread. You don't need to change the code you write because of several distros, browsers (this, kind of, you could actually use browser specific extensions), so they actually affect only themselves. The fragmentation of display servers and toolkits spread all over the place.
Second so you are saying that it would be better if we had one opensource media player, browser, office suite, distribution, de, display server except you approve otherwise in each case. I am sorry that's not open-source. Open source means forking. And of course NO ONE can stop you from creating or forking under gplv3. Don't like it. Don't use it. Don't port your app there. or port it and charge it. I can't see any problem there. Mir's problem.
Are you serious? They started spreading FUD, they made up technical problems Wayland doesn't have. As for being afraid of saying anything, just read god damned Shuttleworth's G+, and tell me he doesn't say almost constantly Wayland is crap. Please. Fear. ROFL. If they are not specific, it's because they have nothing.
Third in every project someone must take decisions. Why should Canonical and Wayland cooperate when there is clearly a direction problem between them. Mir is costing Canonical reputiation and money. Shuttleworth is not insane. Stop being haters and think more before judge anything. The easy solution was supporting Wayland. But was the best? I think Canonical is affraid to say public that Wayland is not viable for them. probably for technical reasons. I strongly believe that Ubuntu Touch wouldn't be in that state today with Wayland. Thats of course mine affair.
And also, a DE doesn't have the drawbacks of forking a crucial piece of software, and actually does things in a different way, but hey, let's ignore that facts.
And last but not least to prove that forking is good i will let you compare today Gnome and Unity. Objectively Unity is more polished, modern, productive, feature rich and as Phoronix proved faster DE. Could Canonical do the same feature changes under Gnome? Of course not! You have an answer why Mir exist now.