People come to Wikipedia to get an answer. Many users of Wikipedia are kids, or non-native English speakers for whom contributing is a challenge. Or laymen that don't know about the subject and naturally don't feel like they could contribute anything. Or people who simply don't know how to contribute. Or people visiting via mobiles where it's really difficult to research and contribute. If you adjust for all those us…
I think that may be a problem for Wikipedia in such countries. People can read/write English good enough that they just go directly to English.
It's pure speculation on my end though. But I'm a non-native English speaker but I never go do my native language's Wikipedia.