First let me say I do not agree with this question being here for Republican's and/or African American Republican's would likely be offended by it for obvious reasons. Despite that I will attempt to answer this.
The Republican Party may have "abandoned" civil rights for African Americans because the party is based off of corporate concerns that do not always align with civil rights for people that, sadly, in some cases, are stereotypically less financially doing well for businesses to take advantage of.