Like Security, environmental engineering had been carved out as a separate field (or fields), but needed to be folded back into the other engineering disciplines. Experts are needed, but some grounding in Environmental Design is required for pretty much any type of engineering, be it mechanical, chemical, civil, etc. Without that background, the afterthought problem sets in. Environmental issues that could be easily avoided early on, in the design stages, are frequently difficult and expensive to address after the products have reached the public. Every engineer needs enough Environmental Engineering knowledge to be able to evaluate their own designs. Similarly, security is a facet of just about every computer science discipline, and needs to be integrated into those subjects. Computer scientists need enough security knowledge to evaluate the security of their own designs, and to recognize when they are in a situation that requires further expertise. Otherwise, security experts will continue to find themselves patching the same mistakes over and over again.
The change in how Environmental design is treated has come about due to multiple different factors.