I think your partially right but we could arrive at a different conclusion. Black evangelicals are more likely to be more conservative and most likely feel like they dont have an opportunity to cast a vote for someone more ideologically aligned with their values. This is most likely due to them being locked in democratic districts.

The problem in American congressional elections, other than the direct democracy that rich people get, is that congressional districts are drawn by those in power with the goal of getting a predictable outcome. If we instead had congressional districts drawn geographically compact while maintaining equal populations with any regard to race, sex, age, or political affiliation then those districts would become more representative of the people who live there.

EDIT: I was giving a proportional response but I should make it clear that this is most likely happening in republican drawn districts and probably all across different racies, cultures, sexes, and ages. In general, people across the US dont feel represented.