Theranos in particular didn't have many _proper_ VCs involved; it was a lot of, essentially, individual dumb rich people (and/or their family offices). IIRC a proper VC turned them down at some point because they couldn't produce audited accounts. At all. Not even from a dodgy auditor. It was a weirdly amateur fraud, when you look at it; an awful lot of it came down to "trust me, bro". FTX was a far more professional fraud, granted.