It's because only white people can be racist, doncha know. Black, Asians, are Hispanics minorities, so in the world of political Correctness, they can be racist, while the act of even asking why no white events is in itself racist.
Imagine a White Miss America, or White Journalist Group or White Congressional Caucus or White health fair. Inherently racist. Any other ethnic or racial group just being inclusive by being exclusive.
Then there's also the patronizing idea of whites never advocating for whites, since they are somehow better than these lowly minorities anyway. The smirks you see posted sometimes when there's a non-descript story of low-level governmental incompetence and how afirmative action was somehow responsible, for example.