Why Does Ubuntu Replace Evolution with Thunderbird?

For those who don't heard the news, the default e-mail client in Ubuntu 11.10 was changed from Evolution to Thunderbird.

I haven't never like Evolution so this is the good news (though Thunderbird is not perfect as well, my default client is Gmail for now).

However, the question is "Why Change?"

After a few googling sessions, here are reasons:

As one who has followed GNOME development for some period, I think Evolution is long dead. It was invented as an Outlook replacement but never achieved its goal. It also fail short on usability front and I know nobody using it for their real life email. (The whole GNOME project is in decline as well, to be discussed next time)

Thunderbird has a long way to go but this change is a good signal from Ubuntu project.