Why were there less blacks in the 46th congress in 1879-1881?

Answer 1

Reconstruction ended in 1877 with the consequence that many of the protections African Americans had benefited from under Reconstruction were repealed locally or no longer enforced. Without the federal government ensuring some measure of equality, many - if not most - African Americans in the South became effectively disenfranchised. Also - Reconstruction had been carried out under the Republican Party. When it ended, the Democratic party - as the opposition to the Republicans - was extremely anti-African American (at least the Southern Democrats were) and seized control of the Southern governments for most of the next century. Since it was so anti-African American at the time they really were not likely to field any African American candidates and since only Democrats stood any chance of election that meant no African Americans were going to get elected. The situation remained that way until the start of the Civil Rights Movement after WW II.

Answer 2

African Americans in 1879 couldn't vote nor run for office even though they had been emancipated since 1867. Jim Crow laws were in full effect in 1879.