Blender export backend missing

[Théo Maxime Tyburn]

Hi,

I want to import and export mesh sequences to Alambic or USD files using 
blender. But these
import/export formats are not available in the import/export interface. 
Although the
version should be high enough, see
https://docs.blender.org/manual/en/latest/files/import_export/alembic.html

Is seems to be because the "WITH_ALEMBIC" option is not used as a
configure flag. I think
about trying to build it myself with this option. Is there any
particular reason this was not added? Can you forsee what should be done
extra to make it work (link another lib or something)? I noticed that other 
export
backends are missing, are they being kept out for the same reasons? 

Cheers,

Théo