My Ukrainian great grandparents were taken to concentration camps in ww2. I’m not Jewish to my knowledge. Why would the nazis take them?

For context I don’t know much about my grandparents so it makes it harder to narrow down answers. I’m not of any Jewish decent that I’m aware of so that takes that partially out of the equation. My great grandmother told stories to my grandfather about how her family was taken from their homes and separated and that she was freed by ally troops. They were Ukrainian and my last name truly shows it. Getting down to what matters now is I’m questioning why they were taken to the camps to begin with. I know the nazis went on massacres throughout Ukraine specifically the einsatzgruppen. I have not truly been able to find a good answer to my question and I was wondering if anyone more qualified had any possible answers. Any help would be awesome!!