Behaviorists could not accept the Freudian notion of inborn traits or impulses, whether called id or libido or anything else. What mattered was learning. A personality theory was not needed. A theory of learning would include all of the details about personality that one would ever need. Behavior is shaped by its consequences.
Some behaviors result in reinforcement and, thus, are repeated.
Other behaviors are not reinforced and thus tend not to be repeated. Consistency in behavior simply reflects the consistency of one's reinforcement history. What matters for one's personality, they argued, was the system of habits one developed in response to cues in the environment. Motivated by drives, habits that get reinforced tend to be repeated and, thus, become part of the stable collection of habits that constitute personality. He claims that many aspects of personality are learned, but often through observation and social influence.