Originally Posted by kmv2

You seem to have answered the question yourself already.

Crap material for one, also crap parts.. most are also missing industry standard dropout locations and stuff that higher end bikes have. Some dep store bikes don't even have dropout hangers. To most, steel is steel and aluminum is aluminum, but that's not always the case. The alloy composition, thickness, geometry all have an effect on the end feel of the ride. There's a reason there are have hundreds of bike manufacturers that all use the same Shimano/SRAM/etc groupsets and usually differ only by frame and fork.

To put it in an analogy, you could buy a Honda Civic and spend thousands do get the performance and handling of a Ferrari on paper, but nobody will ever agree that it meets the overall feel, fit and finish of the Ferrari..