My best guess is that these VCs need to deploy so much capital that they don't really do due diligence, instead they go by "founder vibes" and "vision", a watered down version of "invest in the team, not the product". Sequoia, SoftBank, a16z all seem to be guilty of this.
Anecdotally, Chamath Palihapitiya, in the recent All-in Podcast [0], said that they met with SBF and as a condition to invest they wanted to get rid of dual class voting shares (or something like that) and a board. FTX leadership (not necessarily SBF) replied with "fuck you".
So I guess you have some VCs trying to do the right thing, but if founders can get capital with no strings attach elsewhere, then your ability to deploy that capital is hampered. Essentially, until recently there were was more capital than founders, so founders could just do whatever (and SBF did).
I would expect that this changes a bit with raising interest rates and a tech downturn, but a16z's $350M investment in Adam Neumann's newest Thing makes me think that we are still flush with money ready to be thrown at anyone that has the connections to get a coffee chat in Sand Hill Road.
[0] https://open.spotify.com/episode/3CKYt4mKxndPkEfAvc7SM0?si=e...