He does have a certain unique style that is all Arnie. "I'll be back" just does not carry the same impact when done in a non-Arnie voice.

He has a very unique manner of speech. Pretty much any significant actor does. Localized dubs lose all that.

He might not hit many notes, but he hits them damn well. "Get down!" "Get down again!"

It doesn't matter how much of a hack any actor is, it's an order of magnitude more hacky when the soundtrack is dubbed into another language.

Schwarzenegger without the thick Austrian accent isn't Schwarzenegger.