All the ridges are to provide mechanical strength. Each side of the mold has deep cavities to create the part thickness. Remember in injection molding uniform wall thickness is king. Then it looks like they glue a couple covers on the top for some reason, probably to keep it from looking like an egg crate and to add branding. The overhang on the outlet is merely to provide enough structure to support the G1/4 tap.
I don't get this...wouldn't solid acrylic be stronger than any kind of fancy ridged egg crate structure?

How is injection molding better than milling out of a solid block? Is it cheaper? I must say cheaper is not really in line with TFC philosophy...