The industry is changing as injection plastic molds are less expensive to do. Time is money so the amount of time spent preparing for a brass model gets higher and higher as the customer demands more exacting rivets, bells and whistles. Judging by the success of Sunset/Golden Gates latest passenger trains and Atlas's Zephyr the world of $800-$1000 passenger cars may be disappearing. I can understand Key shelving the Zephyr and F units seeing what Atlas is doing.
Not sure that Atlas or 3rd Rail are in the same league as Key (or Kohs or MMW) nor are they trying to be.
Atlas is nice (as is 3rd Rail) but they are far from state of the art in accuracy and ultimate fidelity. They can't be at their price point as well as the need to make some compromises to make the models for both the 2 rail and 3 rail markets.
Key/Kohs/MMW are state of the art in accuracy and fidelity and have a price to match it.
With that said, the injection molded kits from San Juan Car Company and most recently the SP GS gondola from Jimmy Booth at Glacier Park Models are state of the art.
http://www.glacierparkmodels.com/ACF_GONS_1.html
At the end of the day it's still the same issue whether brass or plastic. Assembly and painting take time and time is money.