Back in the day, Tango Company had at least two purposes: 1) as a holding zone for plebes who were outprocessing during PS, and 2) to offer counseling for those plebes who were unsure about what they wanted to do. Plebes in Tango still had to get up, make their beds, do a modified PEP, greet detailers and officers, etc. But there were also ample opportunities to seek the counsel of the chaplains and officers and senior enlisted outside the chain of command. They've been doing this a long time, and they recognize that while the plebes are now adults, they are also young and inexperienced (I see this with my own students as well). Some of them really haven't had a "worst day ever" yet, and do not (yet) know what they're capable of.
I know my PS company received one plebe who tangoed, then changed his mind before the process was done. He finished plebe year and graduated into surface warfare, stayed in for 11 years before separating.
During ac year, many of those who fall short do so in calculus and chemistry, especially. Those are common freshman-killers nationwide, though. Smaller numbers of academically unsat plebes will struggle with English or history. One of the things USNA offers is incredibly thorough academic help. Mids can get help from instructors through EI, or extra instruction (basically, office hours), through organized tutoring offered by other mids, often within one's company, or through the Plebe Network - you shine my shoes, I help you with Taylor's theorem. It's not that USNA mids are unprepared, it's just that college is hard. It's supposed to be hard. And it's a really different way of thinking and learning than most college freshmen and plebes have been used to for the previous 13 years. In K-12, they had parents making sure they did homework every night, checking their worksheets, maybe checking off a form on their kids' folders. Or parents checked CMS (course management software) regularly. They had teachers reminding them every day what to read and when the next test was. They had time in class to work on assignments, and multiple chances to revise and get things right. They read 25% of what they're expected to read in college. The longest paper most high school students write, ever, is 1.5 pages, and it's heavily prescribed: first paragraph thesis sentence:____. Second paragraph, _____. Etc. They may be the best and brightest, but that doesn't mean they have experience planning their work week based on syllabi from five classes; it doesn't mean they can estimate how much time it takes to work a problem set for calculus or prepare a chemistry lab report; it doesn't mean they know how to write a paper that makes a clear claim and supports the claim with evidence; it doesn't mean they know how to sit their butts in a chair and work at that calculus, really struggle with it and not give up and screw around on Facebook or YikYak; and it doesn't mean they know how to get help, and from whom. I don't mean to suggest they're incompetent because they aren't, and chances are that USNA plebes are probably ahead of the pack on these things. But learning how to regulate your life is a major challenge for most college freshmen, and most USNA mids are not immune to this. I spend a decent chunk of time in my freshman courses just helping students learn how to do life. These are just some of the things that can be roadblocks for plebes.