Lots of aluminum bike frames are already made from hydroformed tubes. Anything that looks like it wasn't just made from pipes, is molded. The question is whether making a frame from a smaller number of molded parts is cost effective. The different parts have to be of different thicknesses, and there's just the geometry puzzle of how to do it without ending up with a big seam that has to be welded anyway.

Early Schwinn frames included parts (head tube, bottom bracket) that were formed from sheet metal. One thing about making tubes from tubing is that there's very little waste.