Karna's loyalty to the Kauravas stems from his sense of gratitude towards Duryodhana, who had accepted him as an equal despite his low birth. This loyalty leads him to fight against the Pandavas, who are the rightful heirs to the throne. Despite knowing the righteousness of the Pandavas' cause, Karna remains steadfast in his support for the Kauravas.
However, it is important to note that Karna's actions are not entirely black and white. He is often portrayed as a tragic figure, torn between his loyalties and his own moral compass. He displays moments of kindness, compassion, and honor throughout the epic, which adds depth to his character.
Ultimately, Karna's portrayal as an anti-hero adds complexity and nuance to the Mahabharata, highlighting the internal struggles faced by individuals and the choices they make, even when those choices may not align with conventional notions of heroism.