The pairing of expectancy and extroversion seems logical since extroverts are typically seen as being extremely outgoing and action-oriented, both of which positively correlates to driving factors of their motivation for high income and success. The research also suggests that most extroverts are extremely outcome oriented and some of the study show extraverts as being input oriented as well (Woodley et. al., 2000). However, a study by Judge and Ilies (2002) found that the personality traits of neuroticism and conscientiousness were the strongest motivators in all three of the process motivation theories, although the personality trait of extraversion was also applicable in all of these perspectives but to a lesser degree.
References:
Judge, T.A. & Ilies, R. (2001). Relationship of personality to performance motivation: A meta-analytic review. American Psychological Association, 87(4), 797-807. doi: 10.1037//0021-9010.87.4.797
Woodley HJR, Bourdage JS, Ogunfowora B, Nguyen B. (2000) Examining equity sensitivity: An Investigation using the Big Five and HEXACO models of personality. Frontiers in Psychology, 6(2000), 1-15.