It's a problem with interpreting risk and control. Allow me to explain:
1. People think (wrongly) that they can control catching the virus. They can wear a mask, keep their distance, etc. This gives them a false sense of security and control. They think that if they do catch covid, they're unlikely to get really sick from it.
2. People (righly) think that they have very little control over what their bodies do after they get a vaccine.
3. People (wrongly) think that very serious side effects are more common than they are.
Those all combine to an incorrect belief that they are better off without getting vaccinated. It's not an absurd sequence of beliefs. It's wrong. But it's easy to see how a lot of people become skeptics.
Point 1 and 3 can both be remedied by increasing awareness. At least in my neck of the woods, official communication has been pretty poor. What's especially lacking is communication aimed at people who are not very science-literate.
When I got my first shot, there was almost zero information about potential side effects. Two weeks later, I developed a huge rash near the injection site. Being somewhat intelligent, I was able to look this up and figure out that it was no big deal. If someone who is already skeptical were to experience this, I imagine they would be very disinclined to get their second shot.