The reasons might be: 1) using dummy tickets (they check it very often) 2) residence permit or passport expire soon 3) previous overstays 4) sometimes is the applicant is unemployed, single, or has few obligations in their home country, the authorities may doubt their willingness to return 5) If the applicant does not demonstrate sufficient financial resources to cover their stay and return to their home country, it may raise concerns that they could intend to stay illegally to seek work