A very cynical answer to what's the logic here: objective measures get in the way of many non-academic college admission goals, so colleges want to do away with them. One of those goals is racial diversity, and that's the only one colleges openly talk about because it's the only one that can positively impact society. Other goals include raising more money by admitting the children of major donors, improving the prestige of the college by admitting top athletes (even when they lack academic ability and motivation), and connecting the college with as many important and powerful people as possible(to bring both money and prestige to the college, and/or to help high ranking administrators make connections).

Of course colleges do all these things already, but imagine how much easier it will be for them when they don't have these pesky test scores showing the students they want to admit aren't qualified.