because he has flawsUsed to give a reason, often followed by a contrasting or emphatic expression such as なおさら, いっそう, or かえって. 欠点 means a flaw, fault, or shortcoming.
JA: 彼には欠点があるからこそ、親しみを感じる。
EN: Precisely because he has flaws, I feel a sense of familiarity with him.