People may choose to stay in relationships that they constantly complain about for various reasons, including:

1. Familiarity and Comfort: The fear of the unknown or the comfort of the familiar might lead individuals to stay in relationships, even if they are not entirely satisfied. Change can be daunting, and some may prefer the security of the known, even if it’s not ideal.
2. Investment in the Relationship: People may have invested a significant amount of time, effort, or resources into the relationship. This investment, whether emotional or material, can create a sense of obligation to try and make the relationship work.
3. Fear of Being Alone: The fear of loneliness or the uncertainty of being single can be powerful motivators. Some individuals might stay in a relationship, even an unsatisfactory one, to avoid the perceived challenges of being alone.
4. Hope for Improvement: Despite complaints, individuals may hold onto the hope that the relationship will improve over time. They might believe that with effort or changes, the issues causing complaints can be resolved.
5. Social or Cultural Expectations: Societal or cultural norms, family expectations, or religious beliefs can influence individuals to stay in relationships. The pressure to conform to these external expectations may override personal dissatisfaction.
6. Financial Dependence: Economic factors, such as financial dependence on a partner, can make it difficult for someone to leave a relationship. The perceived inability to support themselves can be a significant barrier to ending a problematic relationship.
7. Children and Family Ties: For those with children, the desire to maintain a stable family environment or the fear of disrupting their children’s lives can be a powerful reason to stay in a relationship. Family ties, in general, can create a sense of obligation.

It’s essential to recognize that each person’s situation is unique, and the decision to stay in a challenging relationship is influenced by a complex interplay of emotional, social, and practical factors.