While shytting on TLR posters for having bad politics is normally commendable, the premise of this thread is dumb because OP isn't taking Booker's and Harris' past and records into account.
If Elizabeth Warren were to win the presidential election in 2020 and Tim Scott runs and somehow wins the GOP's 2024 nomination, would you expect black people to support him over Warren? Obviously, Booker and Harris are better than Scott, but the premise of this thread is centered around the fact that those two are black and nothing else.
More generally, black voters tend to be the most pragmatic in the electorate. Hillary was outperforming Obama in 2008 with the majority of black voters until they believed he could win (decisively won Iowa and a close second in New Hampshire). So it shouldn't surprise anyone that black voters would have a non-black candidate over a black one. If black voters (or posters) don't think the black candidates can win or don't like their message/records, then why would they support them?
Also, Castro, Gabbard, and Yang are people of color.
Edit: Wayne Messam, a black mayor from somewhere in Florida, is also running (why?).