US Visa Applications Must Be Submitted from Country of Residence or Nationality

I was a US diplomat in India for 2 years and processed tens of thousands of visas. While this change will cause some inconvenience for, e.g., current H-1B visa holders from India who can no longer travel to Canada or Mexio to apply for new visas, in general it makes a lot of sense. I worked at the number one H-1B processing post worldwide. Our post had the expertise to quickly evaluate applications and approve the clearly legitimate ones while scrutinizing the potentially fraudulent ones. We tracked fraud patterns and kept tabs on known-bad petitioners. We could visit petitioner locations on the ground in India. This expertise doesn't exist in Canada or Mexico. Staff at those embassies and consulates would have to consult with us in India, or simply make uninformed decisions. Note also that bona fide residents of a country can still apply in their country of residence.

For a few weeks in India, we had a string of third-country nationals (I won't say which, but it's not hard to find) apply for foreign medical graduate visas. We weren't familiar with the context in country they were coming from. They seemed to be generally good quality applicants and many were approved. It turned out that there was a cheating scandal in that third country, an entire batch of test results had been invalidated, and the embassy located there was refusing their visas, so a few applied in India and were approved, then word got out and more came. We eventually wised up. However, there was really no good reason for these applicants to be travelling from their home country to India for a visa appointment even under normal circumstances (India isn't exactly known for having short visa wait times).

Why not disconnect the reviewer from the submission location then?

Because there is a statutory requirement that applicants who require an interview appear personally before a consular officer. So far, the State Department has interpreted this to mean "standing physically in front of".

Having done tens of thousands of visa interviews, I do think the requirement of a physical appearance before an officer is important. I could quickly review a person's travel history by looking through their passports, questioning them about prior trips. A person's travel patterns and visas to other countries can tell you a lot. I could quickly use a UV light or magnifier on educational documents to see if they were genuine. Several times, I overhead conversations from other applicants and officers that were relevant to my applicant (same employer/group) and I would consult with them. There are many other details you notice when doing this in person thousands of times.

There are also practical matters - if you're trying to do this via video link, how to you authenticate the person on the other end? At the consulate, we fingerprint them and compare them to previously collected biometrics. If you offload this authentication to a contractor site in the US, but I'm in India, is this site open in the middle of the night?

In cases where the applicant qualifies for a waiver of the interview, the State Department actually does (or at least did when I was there) have a substantial program whereby visa applications are largely processed remotely. An applicant would have no hint as to whether or not that happened, though.