I’ve noticed that American movies from the 1940s or 50s have their content “toned down” when it comes to depictions of sex or violence, even in romance where the lead characters kiss (they pause every 3 seconds) with zero nudity except maybe a bra & crime or noir flicks always involving the protagonist/s winning (like the narrative shows police must be victorious rather than admitting defeat towards criminals) to list a few.
On your second question, it’s a little bit of propaganda and a little bit idealism. America was still on a high from the victory over the Axis, Russia was the new big bad, and TV was still very new. So Hollywood and the government wanted to capitalize on that by portraying what the idealic American should be and instill trust in the government. Which eventually came to a screeching halt in the 60s.