Updates of this nature take time. It's no secret that when 5.0 launched it still had bugs. And, when we update our products, we end up finding more bugs that need to be fixed. There are a lot of reasons for what that happen, but, basically, each phone has a unique set of components and a way they interact.
When Google creates a new release, they don't validate it for all the possible combinations there are, and they won't fix anything that's not reproducible on a Nexus device, that's our job.
(Ahí tenéis el por qué no basta con que Google saquee la actualización y hale, a meterlo a todos los móviles del mundo mundial para mañana mismo.)
