This comment about the Houston Space Center's Rocket Garden drew my attention to the cropped image below, from that link.
I'm under the impression that some liquid propellant engines don't have a quite as extensive layer of tiny tubes running everywhere, perhaps more modern ones, or of different designs?
Question: Why do some engines have so many little tubes, and others, not so much?
Cropped and processed from original https://i.stack.imgur.com/IuVM2.jpg from here.