[pjmlp]

Outsourcing might have had an impact, but it wasn't be biggest culprit, everyone outsources nowadays even Apple.

The Register has a few good stories on it.

http://www.theregister.co.uk/2011/11/21/nokia_hildon_the_gre...

http://www.theregister.co.uk/2011/01/12/symbian_history_part...

http://www.theregister.co.uk/2010/11/09/symbian_developers_m...

As you might imagine not everyone wants to disclose what went wrong on public forums.