Because after passing the written test, interview and physical examination, you will receive a political examination (qualification examination) form. The personal information you want to fill in the form, including whether you have a criminal record or not, and your previous work, is generally subject to the content filled in the political review form.
If the organization wants to know the situation, it will send people to the work unit where you fill in the political examination form. If you don't have a job at present, you can write unemployed on the political examination form, and then the organization will send people to your neighborhood to get to know you.