That's the question I would look at. I totally agree with you. I think it's a fundamental question. Why do these differences exist? Why are the criteria different for countries on the same continent? That defies any fair approach. Criteria like this shouldn't be applied, because they're discriminatory, in my opinion.
You mentioned Nigeria, but we also need to look at the linguistic borders within the continent.
According to the studies that have been conducted, fewer study permits are granted to students from French‑speaking African countries than to those from English‑speaking African countries. In my opinion, this is something that should be considered. The linguistic borders also exist in this regard.
If a $30,000 deposit is required, it's even more discriminatory. Since the operating principles are already opaque and discriminatory, it becomes even more serious, in my opinion.