I wish game devs focused more on finishing the game before finding and paying for voicing... perhaps that could help finalize chapters or segments faster.
They did what you described.The story for Season 2 was finished way over a year ago. Voice acting was added long after it was finished (and in the meantime one of the actors quit, they had to rerecord all of her lines).
What a lot of people don't seem to understand, is that in the "developing" process not all do the same or can do the same.
The one doing the voice samples may have no programming skill at all, the programmer can't write stories.
While the voice director is still busy recording for S2, others write and render for S3 or one of their other games, while programmers put already written and rendered stuff together, create a build pipeline, fix bugs or whatever.