It works that way cause the pressure builds up at each end point and will continuously flow based on usage after that. If you have it all in one pipe and that pipe is full pressure back to the start, only a very small amount of water will travel through it to the end, and if that small amount of water is the only thing flowing you're only gonna hit like 5 hydroponic tiles. On my current base, I have my first hydroponic farm set up on the same pipe that runs to my toilets and showers, keeps everything moving, but when I make another farming room it'll have a setup like that most likely.