One of the problems with Blender for high-end pipelines is its license. High end studios often create specialized software and addons for their pipeline. Because of the Blender license, anything they create for it would have to be released to the community. Some studios could conceivably avoid that just because it would give insights into how they do things in house, and they don't want to share that with their competitors. More likely though is that releasing it to the public would mean they spent their money to develop a tool and then had to give it away to everyone. They would be essentially giving their money away, or at the very least, they would literally be developing those tools for their competitors to pick up and use.
Another problem with it is Blender's notoriously bad file interchange with other applications. It only just got a working FBX binary I/O, and it doesn't support Alembic, which until recently made it pretty useless downstream from the application used to create animations that are to be rendered. Lastly, it's NURBS support is laughable, and a lot of stuff for movies is done with NURBS. If those assets have to go through Blender, you have to bake all that NURBS stuff to polygonal meshes before taking it to Blender. In the case of things like wires, hoses, robotic tentacles, etc, that means you would have to rig those things to recapture the movement/deformation functionality you already had with NURBS. That takes time (which would not have had to be spent if you had stayed with NURBS), and time quite literally is money in professional production.
I'm sure there are other things, but those are the two biggies that I know about.
Also, Z-up? Really? At least code in the ability to swap that shit.