Popularity plays a role. Here's a real life example: One of my quantum physics mentors submitted a paper to PRL (a high prestige physics journal) and it was rejected. Why? Because it came from a small, rather unknown university in Spain.

He was later admitted to Cambridge for a PhD and sent the exact same paper (same formatting, content, layout but different department/uni). It was immediately accepted. Does it necessarily mean that scientists in poorer countries are doing bad science? Or just that they didn't get their visa / couldn't leave their country / just want to stay there, etc.

The first filter most editors use is: "Do I know this research group? Are they part of the club? Have they published in top journals?". If not, it won't get read (unless it's a compelling and exciting title and abstract).