I can see how that explains the 3-year service minimum, but I'm not sure how that explains the field-of-study restrictions. Once you're there for 3 years, why do they care which courses you enroll in?

Ostensibly because high demand fields are more likely to get hired and lead successful careers outside of Amazon.

Logistically it also simplifies things because you can respond to "Why can't I pursue education X?" questions with "because the BLS doesn't list them"

I guess I'm still confused why that matters to Amazon, unless it's part of some world-bettering mission. Wouldn't it be logistically simpler to say employees can enroll in any course offered by the state community college system, and wash their hands of it past that? I mean, they're just offering a perk as part of a compensation package, it's not like they're supposed to be their employees' parents or career counselors.