*Disclaimer - I work in VFX*
The issue with anything that's expensive in film is that people get paranoid about wasting the money and want to plan shots to the N-th degree. Which wrings the last drop of creativity and spontaneity out of the shoot.
With VFX, the shooting order isn't just 'Storyboard' > ''Acting rehearsal, Set design, Blocking" > "Shoot". There's a 'previz' stage after storyboarding which means they plan every shot in excruciating detail and replicate it in 3D before shooting the plates. Then edit the previz together into an animatic to previsualise every VFX sequence before principal photography.
In VFX-heavy blockbusters, things end up with the tail wagging the dog. A bunch of VFX vendors, being paid a huge chunk of the budget, start to dictate how the film will develop. And a director telling VFX to revise things for creative reasons results in the VFX equivalent of a domestic plumber shaking his head and saying 'ooh, you don't wanna do that, that'll be expensive'.
Friends often say to me 'why didn't they spend a tenth of the VFX budget writing a proper script'. But the VFX dept has already made changing things for creative reasons into turning a supertanker at sea.
(And don't even get me started on the fact that VFX isn't even unionized, which is why the 500+ vfx roles end up right at the end of the credits after 'drivers', 'caterers', 'genny operator', 'greensman' (gardener), 'insurance' etc.