Does anyone know why?

The current official rationale: https://wiki.ubuntu.com/Mir/Spec#Why_Not_Wayland_.2BAC8_West... https://plus.google.com/113883146362955330174/posts/PXc93m8n...

For the history, abandon all hope ye who enter here:

http://www.phoronix.com/scan.php?page=news_item&px=MTMxNzI https://wiki.ubuntu.com/Mir/Spec?action=diff&rev1=3&rev2=4 http://www.phoronix.com/scan.php?page=news_item&px=MTMxODY

Copyright assignment.

Neither Wayland nor Mir require copyright assignment

Look at the fine print when you contribute patches then.

For individuals: http://www.canonical.com/sites/default/files/active/images/C...

2.3 Outbound License

Based on the grant of rights in Sections 2.1 and 2.2, if We include Your Contribution in a Material, We may license the Contribution under any license, including copyleft, permissive, commercial, or proprietary licenses. As a condition on the exercise of this right, We agree to also license the Contribution under the terms of the license or licenses which We are using for the Material on the Submission Date.

Same goes for the entity license: http://www.canonical.com/sites/default/files/active/images/C...

You might also want to read the following:

http://mjg59.dreamwidth.org/25376.html

Yes, but that's still not assignment of copyright. The contributor still retains their copyright.

Fair call.

It has been implied that it's so other devices couldn't as easily implement their 'convergence device' idea as they could have with Wayland.

Wayland wasn't ready

That doesn't make sense. At the time, Wayland was more ready than a project written from scratch. Their initial manifesto also called out a bunch of things as failings of Wayland that were patently false. The Wayland core devs also did not know that Ubuntu was having these issues, IIRC.

So either:

1) Ubuntu didn't understand Wayland at all, amd decided to write their own from scratch without talking to or consulting the Wayland devs.

Or

2) Ubuntu has an ulterior motive (e.g. Not-Invented-Here-syndrome).