Bad examples. They were produced during 2.8 development.
Spring was basically a test for 2.8 depsgraph, collection workflow, etc…
Hero is the act of birth of Grease Pencil as object. Almost all GP improvements made in 2.8 was done for the movie or used a resource from the movie as a demo file.
Elephant Dreams simply installed basic pipeline to make movie. (groups, render layers, etc…)
Big Buck Bunny added basic extras like Fur, Volumetric Clouds, Approximate AO.
Sintel was made during 2.5 period. Same as 2.8 period movies, a test in production and development of lots of new 2.5 tools and a resources provider.
Tears of Steel was a motivation for addition of motion tracking and masking tools.
Caminandes was used as multiview demo.
Hair shapekeys of Cosmos Laundromat did not end-up in 2.8 but all the other features developed for Hair (hair cut, new hair dynamics) did. Plus a lot of features like dof, screenspace AO, backdrop for compositor and sequencer, beginning of OpenVDB and Alembic support…
Glass Half was planned to be a proof of concept that a movie could be made simply with OpenGL render.
Nobody expected new features from that but just resources.
Agent 327 brought lots of optimizations and demoed all improvements made by Cycles during 2.7 series.
Open Movies are really bringing new features when artists are inspired. But of course, it was more obvious when Blender was smaller. And during big projects of development like 2.5, 2.8, it is not easy to clearly attribute a new feature to team of open movie or member of community testing new stuff.
I would like that during such period workload for devs will not be pushed too far by launching a movie production during same period. That is bad for new design and for the movie.
But clearly, open movies are useful demos and resources providers for the cloud.
This is also more work. They did one open game : Yo ! Frankie !
Its files became obsolete a lot faster than for an open movie.
It will be easier to produce a game that looks like Yo! Frankie! now. Tools are more efficient.
But to produce an AAA game with standards of 2020, you will need a budget for an AAA production.
It is already difficult to find millions for short movies. How could they find billions for such thing ?
The contribution from Epic Games is filling the gap that was existing according to dev fund page to bring amount of developers working full time on Blender to 10.
That is a great news when developers are expressing their frustration on working on a complicated task like a new design like 2.8. It will help them to focus on other aspect than financial worries to accomplish 2.8 design.