Look, "in principle" stuff is not how the real world works. AFAIK, hacks happen mostly because of carelessness. No one cares because no one cares if they care (and the compensations etc reflect that). I know enough such cases in fintech (forget about other verticals), which are mostly stupid like wrong RBAC, open firewall, AWS keys taken by roommate etc and not public of course.
https://www.nbcnews.com/tech/security/former-twitter-employe...
There are certain security measures which can minimize insider threats. But ultimately it's just hard to guard against agents who are willing to commit felonies in order to carry out their missions. Even defense industry companies which have tight security over classified information have been repeatedly penetrated.
The upper bound of security is unable to make attacks with a 10 M$ return unprofitable. Raising the lower bar just raises the barrier to entry for new participants, it does not stop existing ones.
Most attacks do use basic techniques since a 10 M$ payout on 10 K$ cost is still better than 10 M$ payout on 1 M$ cost. No point wasting the good stuff when the basic and cheap stuff works just as well. But if you get rid of all the cheap ways in they will still attack using the more expensive stuff since the payout is still wildly profitable.