I got the flu in May 2019. Not hospitalized, but not a quick recovery. I'm a little scared of Covid-19. Wearing a mask for a half-hour of shopping is a good balance. My most people in my home town won't wear a mask--despite my home town having the highest Covid rate in Canada at one time.
Here's my hypothesis. The highway speed limit in is 110 km/hr. Many people drive 10 km/hr over that limit. That is where the police start giving out speeding tickets. And that is the deterrent.
Very few speeders want to recognize the increased danger they put themselves when travelling a little faster. They can't fathom the tradeoff between increasing their 0.000001% to 0.000002% chance of having an accident, the lifelong effects of that accident, and saving maybe 15 minutes of a two-hour drive.
In a like manner, young people are really not affected by Covid-19. When the risk is low, people tend to ignore the consequences.
The psychology behind speeders and not wearing a mask is very similar. We human beings are not very good at evaluating risk.