unknown1961,
BLUF: Non-techs way under-index for Types 1 & 7 but over-index for Type 2; techs way over-index for Type 1 and slightly over-index for Type 7.
Best explanation would be that it's about yield. Higher yield by steering Type 2s to non-tech and Type 7s / Type 1s to tech.
Longer version:
Per the 2013 RAND study of the HSSP program and staffing needs of the Air Force, of the applicants who passed the initial AFROTC HSSP screen for SAT scores -- roughly half of whom went on to be interviewed -- ca. 65-68% intended to be tech majors, 25-28% were non-tech and 7% were foreign language majors.
Of those who were awarded scholarships, ca. 75% were tech majors, ~9% were foreign language majors and only ~16% were non-tech.
So, OVERALL, for applicants with similar SATs, the non-tech applicants under-indexed for winning scholarships.
Interestingly, for winning Type 2 scholarships only--not for Type 1 or Type 7-- the non-tech applicants' success rate was right in line with (or even slightly above) the index ie about 30% of Type 2 were non-tech.
For Type 1, 99.9% of the scholarships go to tech majors. If you're not tech, you won't get a Type 1.
For Type 7, there's a significant bias against non-tech and a slight bias for tech and for foreign language.
You can win a Type 7 as a non-tech with a strong profile, but it appears that the process is somewhat more likely than expected to award a Type 2 to a very strong non-tech applicant.
I suspect, but can't prove, that the logic here is all about "yield" ie ensuring that the applicant who's awarded a scholarship will actually use it.
Here's how that logic would work: non-tech applicants in general may be more likely than tech applicants to seek to go out of state. This would be because of the gap in quality between the top-tier national universities such as the Ivy+ schools, which for reasons of history and cultural bias tend to be outstanding at the gentlemanly "talking" subjects (History, English, Philosophy) and not so strong as the great land-grant schools and polytechnic schools at the "non-gentlemanly" applied sciences and engineering.
So if you're a tech applicant, your local state university may actually be more competitive than an Ivy+ or other "elite" national institution--especially so if you want to study, say, Aerospace Engineering or CS. You can get a better education in those subjects at any one of dozens of state institutions around the country than you can at Harvard or Yale.
Hence the logic in giving proportionally more Type 7s to tech applicants and proportionally more Type 2s to non-tech. Just a theory, but seems logical.