To cut a long con short, Theranos' technology, which was never peer-reviewed, simply didn't work the ways Holmes continually claimed. Between dozens of articles by Carreyrou and an investigation by the FDA, it was determined that an Edison diagnosed your blood about as accurately as spilling it on some bird bones and consulting an augur, mainly because a pinprick's worth of blood isn't enough to get accurate results. Medical labs don't drain entire vials out of you to feed secret hospital basement trolls.
And Edison test results weren't just unreliable; they were potentially life-threatening. Patients could be told that they were peachy when they were at risk of internal bleeding, blood clots, or other major problems. Even worse, Theranos ignored obvious problems brought up by their own quality control checks, because who cares about a few dead people if they get you on the cover of Glamour?
Wall Street Journal
"Well, the hospital tests didn't even detect her midi-chlorian levels, so who are you going to trust?"