- The forms themselves are poorly designed (needlessly complex, come with misleading/incomplete instructions, tons of "gotchas," etc). Between me and my wife we have three degrees and a masters, are native English speakers, yet we still had to Google to figure things out.
- Instead of having one form, they have three, and you cannot submit the latter two until the proceeding one is accepted (even if they're completely independant). They don't actually check the proceeding forms until the visa is complete (we know that because they flagged something months later).
- Paying fees is a nightmare.
- Even their embassies know how terrible it all is. They often hold workshops for people going through the process and are pretty frank about the bureaucracy. They describe the NVC as a "blackhole" (where things often get lost/delayed/mistakenly rejected).
Digitalisation is useful but the US's house is in such disarray that it seems like the tip of the iceberg. I legitimately believe that the US uses bureaucracy and delays as a way to discourage people from applying for visas and or push visas into the next calendar year. It is the only explanation that makes sense.
To be honest the entire US visa process could be done, end to end, in one day if they wished (ex. background check). And in fact US embassies in exceptional circumstances actually do accomplish the entire visa in 24-48 hours (yes, even for immigration visa).