Why can't people accept responsibility

[CannotConnectTryAgainLater]

Man at work was asked to do something months ago but didn't do it, now the job is critical and instead of owning up, he has created a complicated lie to cover himself. I have the info to prove he is lying but I didn't out him. We've got time to fix the problem, fortunately, so have left it.
A different colleague was given some new project info that could be shared with other team members but didn't. Communication was bad overall. When confronted, she said well I've emailed about this recently. The last email sent regarding this was in September.
Why not just say, ok I'll get this sorted straight away, instead of lying/ twisting the truth? Aibu to get annoyed?
Sorry couldn't give anything specific as it would be too outing.

[Nettletheelf]

It’s not unreasonable to be annoyed. The truth is, at least 50% of your colleagues will be at least partly incompetent and will lie to cover up mistakes. Why? Because they realise they have fucked up and are terrified of ‘getting into trouble’, like children.

Only a tiny minority of people will own up to their work mistakes, and those people should be cherished. Most will pretend it isn’t happening and, if you out them, will hate you for the rest of their lives!

[CannotConnectTryAgainLater]

Also this colleague, also lied about having to update all her records due to someone making a mistake. I'm on the team and know that nothing has to be done, she was just trying to make a point.

[Nettletheelf]

The thing is, where people repeatedly lie at work, colleagues always find out eventually. So very often people like that get their come-uppance without having to be formally outed.

[blueshoes]

Sure, there is lots of incompetence or indifference around but it takes someone quite special to lie. I generally don't make a big deal if someone fucks up (what is the point?) but will seriously despise anyone who lies.

Apart from one subordinate whose contract I did not renew, I have not encountered lying much in my workplace. That said, a disconcerting number of my aupairs lie when they say they have done a task. If someone lies, it means they are not prepared or care enough to own a problem. It is just a lazy and cowardly way to conduct oneself which I see as a fatal personality flaw.