Historically, concerns about "diversity of backgrounds", "well-rounded" candidates, and the even more nebulous "character" were code for the fear by the majority's elite of an overrepresented minority gaining entrance into that elite. In the time when these policies were first promulgated the target was Jews [1], but the strategies and motives seem not to have changed: the presence of enormous academic success among an immigrant minority group without high economic status is resented as somehow a "gaming" of the system that needs to be corrected by introducing subjective factors into the system.

Where this gets politically complicated is by the concurrent policies in favor of non-Asian minorities, but at least there the policies are quite explicit about their justifications (correcting historical disadvantage).

[1] http://en.wikipedia.org/wiki/Numerus_clausus#Numerus_clausus...