Widespread pre-emptive testing was not what Theranos tried. Defrauding investors that the technology existed for widespread, inexpensive pre-emptive testing even at small scale is what Theranos tried.

There is almost certainly gold in them hills if you dig deep enough and survey systematically enough, but Theranos started with precise coordinates, claiming they'd "found it", and demanded investors for a mine, while privately they were thinking "If we don't find it on the surface, who cares, we got paid, this is how VC works".