This question already has an answer here:
Related to this question, in The Terminator we have this dialogue:
REESE: Pay attention. The 600 series had rubber skin. We spotted them easy. But these are new. They look human. Sweat, bad breath, everything. Very hard to spot. I had to wait 'til he moved on you before I could zero him.
From this and other dialogue, we are told that the Terminators are infiltration units, designed to look and appear human. In this way they can get back to the human base and start shooting, thus wiping out large amounts of resistance members.
But when you look like Arnold Schwarzenegger, you don't exactly blend in. The resistance was not made up of giant musclemen, but weary ordinary humans with a lot of courage.
We know that Skynet eventually learnt its lesson, making units like Cameron and the T-1000, but why make a giant muscle guy? Wouldn't it just grab a resistance person and make a copy of them?
Looking for canonical answers please. Also, that deleted scene from T3 doesn't count. The T-800s had more than one face.