People are negative biased.

When you experience something you dislike or causes negative feelings you are more likely to remember it.

Combine this with the dunning krueger effect. Where you can only recognize knowledge similar in understanding to your own. Once you go a few percentiles out in any direction on any topic it's hard for you to tell if the person is an idiot or a genius.

So when you experience things far outside your understanding you are more likely to assume that the situation is something you understand. That the person is an idiot or not very intelligent. Rather than assuming you don't know enough to make a valid judgement.

Then you pretty much forget every single average interaction.

Meaning that far from being prudent, cynics are lazy who fall for their biases. And realists who say the world is overall bad aren't really realists. Reality is chaos.

The printing press greatly increased the ability to spread knowledge. Not all of it was good but the increased flow of knowledge helps to further the education of everyone. Although it always comes with an increase in false information. More information is available overall and that's the important part.

It would be incredibly foolish to assume that with the greatest flow of information ever in the history of the world we would becoming dumber.

It's far more a different phenomenon. With globalization we can hear the stupidest stories our world has to offer. This gives an even greater pool of stupid to draw from. Making it seem as if the average person is stupid. The average person is average and has the capacity for genius and stupidity in various contexts.