The reason we know about Theranos is because they took the grift up to a huge level and went from grift to outright fraud once they had to show actual results.

It is not only not unique, but in fact extremely common for startups to be grifts around impossible technical promises, live a few years off gullible investors who have way more money than sens and/or for whom losing a few million dollars on a long shot is just as bad as me wasting a few dollars on a gizmo off Temu I know probably won't work, and which then die out because their ideas obviously couldn't work.

They even sometimes find a niche by pivoting to some vaguely related tech. Say, while flying taxis obviously won't work, a startup trying to build them might find itself developing into a small company building helicopter propeller blades for some specific niche.