>Applications have default admin users.
Yup. And after install, they should be tested. Default non-admin users should also be tested for the basic thing to ensure they are actually restricted and can't do admin things.
>Nobody saw log4j for 15 years. Hindsight is a great thing to have.
You are moving goalposts here. Nobody mentioned log4j issues. The issues being discussed here do not require hindsight.
Confluence left a hardcoded password. At the point a dev is harcoding an f'ing PASSWORD, alarms should be going off with flashing lights and everything. If an auditor isn't searching the codebase for something simple like 'password = ' to see a hardcoded string, then that's a weak audit. The fact no internal code review didn't catch this is also not a good sign.
100% agree no single person can imagine every single scenario that would potentially cause problems down the road. However, when new things pop up, they should be added to a list of things to check for not an immediate throwing of hands in the air with a "we don't do that kind of thing". Instead, admitting it was checked for because it was such an out of consideration thing, but then saying "we'll keep that in mind for future testing" would have been a much better thing response than a bunch of whataboutisms.