On the contrary, the majority of top streamers and casters of CoH are native English speakers (HelpingHans, Stephenn, Siberian, Inverse, Xcom, AmiPolizeiFunk, Tommy, RnP, A_E, VonIvan etc.). Clearly, every rule has exceptions, but you will find a similar pattern within succesful competitive games.
For some reason I was thinking we are talking about CoH2.Besides HelpingHans and Siberian (great streams, btw), not many of those named are still streaming actively CoH2. On the caster side, I see ImperialDane, which has an excellent cast, but his native language is not English. Also, if you think a bit further and remember the fact that CoH2 is not only sold to "native" speakers, but globally, your statement gets even less important. I have not encountered one fun cast/stream where language was a problem or the fact that I did not see the person talking. Usually, the content and the presentation decides if the cast/stream is worth the time.