Steel tubing is a bad idea. $2k for a frame + another $2k for heat treatment and grinding. Not to mention the welding and trucking this thing around! (And how do you get the level under 12ft of linear ways?)
I guess we wanted to "pour" the entire thing like the home buiders do. (yeah..I know...)
8020 came in later, to save money and give the E/G structure a spine.