The only aluminum bikes I can think of with non-track horizontal (road) dropouts are the Raleigh techniums and early C-dale crits. Neither are current designs.

Don't ask why aluminum. You may as well ask why fixed? why geared? why carbon? why SRAM? Why anodized? etc etc. Every time somebody asks about Alu frames or Loose hubs or external BBs (basically anything that doesn't fit a narrowly defined canon of unassailable fixed gear parts choices) some genius just HAS ask why?