I think that there are a few factors at play here : (1) English being the language of international scientific communications, a clear advantage is being given to a few countries already, which all happen to be "developed" (for whatever this means). The comment you often get "improve the English/have it seen by a native speaker" comes as a first barrier (I have had this comment before even on manuscript written by a native speaker of English, so, no worries...). (2) Secondly research needs funding, not all research, but research that is "sexy" and will be published in "high-impact" factor journals. I have moved to Japan, a country where despite appearances funding are very difficult to get and equipment hard to buy... equipment without which publications are difficult to produce. (3) finally (and there is certainly more) there is the Gold Rush effect (I wrote about it with a colleague) where individuals from "developed" countries secure a budget to go and collect data in other/often not so strong economically countries and publish the work instead of the local researchers who could have ripped the benefits (for themselves and their communities). Issues are plenty, but money and intellectual imperialism are certainly two tof the main factors of the problem.

Things will change as the world economy change. Asia is the new white (and a better one).