Organizations with good quality programs know how to assess their suppliers, including those who are ISO/ANSI certified. There’s a lot of information that goes into evaluating a supplier beyond just asking them if they certify their material or have a quality program, including doing site audits. Things can still fall through the cracks of course, but it reduces the probability. I bet if you asked them why they don’t evaluate each lot before the mishap, at least some would claim it’s redundant and unnecessary because the supplier already certified it.
I guess the difference is that not double checking your components is a rookie level mistake, properly vetting vendors is a sophomore level mistake.
The other failure (non-mission) was when they discovered a real unkown-unkown about COPV tanks and helium tanks in near 0-kelvin temperatures.
So yeah, they should not have made that mistake, but its also the case that nobody has a perfect record. Considering the errors most rocket companies have made, theirs seem fairly reasonable.
SpaceX is also pretty good about eliminating checks that have become redundant or otherwise redundant. For example they no longer do a static fire on the launch stand before every flight.
The big promise of Starship is the quantity of flights they envision. A thousand flights will give huge insight into reliability, insight that space flight has never had because most articles are never recovered and inspectes.