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).