Not really. When performing clinical trials, if you'd like to use the results of the studies in chinese/indian populations you'll need to prove bioequivalence in many cases, so you're going to need to collect a meaningful sample in the first place.
The reality is that most clinical trials aren't successes. If you can get a huge cohort of people for relatively cheap elsewhere, you can screen a lot of promising but doomed tests at a cheaper price point, then only re-create similar testing on the most promising candidates in your lucrative markets.
What the grandparent post was referring to as "obvious reasons" must be the high prevalence of HIV in the study countries[0]. Why wouldn't they test in countries with the highest infection risk?
There may be common reasons to trial there like it being cheaper or less regulated. But there is a good reason for this specific medication to be tested in those specific countries. Criticizing the study authors for being "cheap" is uncalled for in this case.
I'm not sure developed countries are the most lucrative market for HIV vaccines. How many people would even get them and why? This is a product almost entirely developed for Sub-Saharan Africa so it only makes sense that they focus on testing it there?
Hard to say, maybe it's not inconceivable that ~1% of potential patients in the US/EU/etc. might end up paying more than > 50%-90% of the people living Sub-Saharan Africa for whom getting the vaccine would make a lot of sense.
The reality is that most clinical trials aren't successes. If you can get a huge cohort of people for relatively cheap elsewhere, you can screen a lot of promising but doomed tests at a cheaper price point, then only re-create similar testing on the most promising candidates in your lucrative markets.