In my era, it was extremely holistic - SATs, grades, recommendations, essays, interviews, extracurriculars, awards, personal stories, everything. Race helped but it wasn't the only kind of affirmation action - they were also targeting women, they were targeting people from less represented states (you had a better shot if you were from Wyoming than if you were from New York), they were targeting people who came from particular sub-cultures and hobbies that they didn't have represented.
All that said, SAT and GPA still ruled. If they saw an application with a 4.0 GPA and a 1600 SAT and knew nothing else at all, that student is almost certainly getting in (but not 100% guarantee). 3.9 GPA and 1500 SAT, then they have a pretty good shot still but maybe it's 50-50, you better still have some impressive awards or competitions or took a shyt ton of high-level courses or impress with your essay, otherwise there's a chance you'll be on the outside looking in. 3.7 GPA and a 1400 SAT, then you better be competing in national science fairs or be one of the best divers in your state or be the only Black kid from Jackson with your numbers applying to their freshman class that year or SOMETHING that elevates you above people with better basic stats. And if you have a 3.3 and a 1300 SAT, then you're only getting in with an Act of God.
That's like asking why Native Americans don't set up their own financial institutions the way the Jewish folk have. There is an EXTREME disparity of resources that they're starting out with to get to that point.
People try and talk like Asians are just 6% of the American population, but that's a misguided way of thinking about it. Asians are 60% of the world's population, and for the nationalities that we're talking about when we talk MIT (primarily China, Korea, Japan, Taiwan, India), only the cream of the crop is even ending up in the USA. That's not just those with the most financial resources, but those with the best education, the best connections, the most entrepreneurial, the deepest drive. Cherry-pick the most elite 0.5% of a group that's 4 billion strong, then of course they're going to have the financial, educational, and social resources to produce elite "college material" on a regular basis. But the global population of African-Americans is 100x smaller than the global population of Asians, plus even on a per-capita basis the resources aren't remotely even at any level. Thinking a similar approach would work is statistical naivety.
"Continuous SAT and after-school programs" can only do so much. The Asian kids putting up huge numbers aren't just doing SAT/after-school programs, they also had highly-educated parents who had time to constantly drill the right stuff into them from an early age (or keep them around people who would). They also had social connections where they were constantly surrounded by doctors/engineers/lawyers/businesspeople who had all been through it before. They also attended schools where their classmates had done the same. They also (in many cases) had personal consultants that they've paid anywhere from $10k to $100k to fine-tune away their weaknesses and maximize their strengths. And even with all that, the VAST majority of those Asian kids going through that stuff don't end up as MIT material - it's still just the cream of the crop of even them who are doing it. 250,000 Asian-American kids graduating every year, another few million overseas Asian graduates out there every year trying to get into American colleges, and only 500 of both groups combined are going to end up at MIT.