Netflix has handed down a lot of surprising cancellations recently, including some shows that had already been renewed, and the cost of Mindhunter evidently wouldn’t have been justified by the size of the audience.
The same kind of cost/viewer ratio is reportedly what led to GLOW’s cancellation.
David Fincher’s black-and-white feature film Mank has been attributed as the cause of delays on more Mindhunter for a while now, and now Fincher apparently feels that there’s not a future for Mindhunter.