Rym, I think the reason why you're seeing more color Con books, and will continue to see more is because it's no longer very cost effective for a printing company to take on black and white work that is a more limited run. The people selling the printing have probably started to take the option of B/W printing off the table. It's just not as useful to many of the people who get the short runs, things like brochures and the like.
I would imagine most company's 1 color presses are older and they have probably been supplanted in ease of running by presses that have computer-controls and computer tools to help them manage the colors, so it's not as energy intensive to print in full color.
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I know several months ago the printer that Kenzer and Company uses to print KoDT had their old web press die and they had no desire to fix it. so, K&C had to change over to a new printer.