Because folks like us are fighting a protracted rearguard action which has prevented our side from being totally defeated?
I’ve found that a pistol usually works.
The reason is that our brains are able to make sense of pretty much anything that’s internally consistent, so it’s possible for very smart people to be very ignorant on any given topic.
As others have said, mental laziness is the biggest problem: in order to not be ignorant on a given topic, you either have to have been exposed to the ‘correct’ information from the get-go, or you would have to have been exposed to nonsense and be willing to seek out and correct your own ignorance.
Personally, I believe that our final salivation will be realizing this and teaching children critical thinking as the standard framework supporting any other specific knowledge. Our knowledge of the world is continuously increasing, so even if we all knew what was what right now, that wouldn’t help with how to fight ignorance going forward. We have to embrace and admit our own fallibility and make sure our children have the desire to self-correct their beliefs.