Because English Wikipedia is by far the version with the most readers, and therefore the one where most time has been invested in making an article good. In my

Because English Wikipedia is by far the version with the most readers, and therefore the one where most time has been invested in making an article good. In my experience, non-English Wikipedia articles are great for "insider knowledge" about topics and/or local figures who are deemed not relevant enough to the English Wikipedia editors. But outside these niches, their texts tend to be both shorter and less polished.