You're making a hubris-laden assumption coders know the gaps their baking into their software — that any human has a decent enough grip on the multitudes of spinning logic duct taped together to make the internet run. Most vulnerabilities aren't "ignored"; they're in a neverending backlog or unknown.

If you closed all of the AI-discovered security vulnerabilities tomorrow - by the next day there'd be a host of new ones. That's software, baby.