Advertisers call the shots and pay for your ad-supported programs. If they want to reach viewers who speak Spanish, French, or Hindi, that's what you'll see. Just because the program is in English, many multi-lingual people may be watching.
America has never had a statutory national language. The founders made a deliberate choice to avoid that so as to welcome all comers. Yes, English has been the predominant language; but plenty of native born and naturalized Americans speak many other languages, often in addition to English.
