It's a hot topic for companies to do the right thing now, its then they start to care.
I don't think its done on purpose or with a hatred, but its an issue, look around.
For women for example you can see from the numbers that there is no bias in the acceptance rate, the thing is that very few women apply. Could be the same for hispanics. I don't know what proportion of engineering students are hispanics but it's likely that as for women the underrepresentation starts already in school.
What evidence is there that proves an equal percentage of every race and gender leads to a more profitable company (or has a higher chance of a successful exit)?* *Because I assume that by listing "UNDERREPRESENTED FOUNDERS" YC wishes there were 50% female founders and 50% male founders? And what about the racial makeup of founders? Is the ideal world for YC a racial make up of 20% white, 20% black, 20% asian, 20% middle eastern, and 20% other?
The decision of who to fund may rely in part on seeking people similar to oneself and if the demographics of the applicant pool are not reflected in the staff of YC it may skew the outcome against minorities.
Well I suppose it's not impossible.