I agree. I've wondered if a producer would succeed if they offered a basic model at a basic price, then offered various option packages to detail the product. Something as simple as little baggies containing detail parts. For a diesel locomotive, option package "A" could be basic parts like lift rings, grab irons, hoses. Option package "B" could be more proto specific details. All to be applied by the modeler. Even include a small disposable tube of factory paint so the color will match, and 2 drill bits.
Don't know if that would be viable, but it does seem that the producers are all targeting the same customer. Walthers/Proto, Atlas, Athearn, and BLI all offer highly detailed, fully assembled models; and seem to compete over announcing new models on a regular basis. I don't know if there are enough of the same type of hobbyists, who are looking for the same type of product, to support 4 different producers of nearly similar products. Only Bachmann offers a slightly different product combining low detail plus DCC/Sound.