What I'm looking at here?
This is a picture of my guest bathroom sink, and the hot and cold inlets are each connected to two or three seemingly redundant lengths of copper tubing:
My first guess is, the plumber who built this in 1978 needed to add stability and, being a plumber, used what was handy. But that can't be right, can it? That's a lot of wasted solder, considering a 2x4 and a couple of nails would have probably accomplished the same job.
The kitchen sink plumbing has the same feature.
That's a manifold and those other pipes go on to feed other devices.
Very likely that the plumbers ran one 3/4" copper tube to the room, then branched off there and ran the other 3/4" and 1/2" pairs to feed other things in the room or in adjacent rooms.
You even have one more cold than hot, which suggests that it feeds a toilet.
Update to add context: In slab-on-grade construction where the piping is under the slab, this is common and it is much cheaper and easier to run one or two long runs back to the place where the water enters the house than running homeruns to every water-using device.
The decision to run the pipes in-slab rather than in the walls? I don't know the reasoning behind it. I just know that I've had homes where the piping is underslab, and homes where the piping is in the walls, but I couldn't tell you why.
I don't have code requirements handy, but there was another question here recently that was similar, and the answer there was that plumbing code did not allow copper pipe joints to be embedded in concrete, so all soldered joints needed to be above the concrete. It looks like you're in a similar situation on a concrete slab, so likely this is the same rationale.
