(D) and (E) are both incorrect because they are not relevant enough to the claim that the argument is making. This claim is that "the perception that [direct-mail advertising] is bad for the environment is misguided."
The idea expressed in (D) - that direct-mail advertisements are targeted - is not enough to tip the scales in additional support. The passage states that "because of direct-mail advertising, millions of people buy products by phones or online," which would very likely outweigh any waste caused by sending direct-mail advertisements to average people who may not be interested. Therefore, if (D) were untrue the argument would not be significantly altered. In turn, this shows that (D) does not add significant support to the argument.
Similarly, (E)'s claim that products purchased through direct-mail advertising are comprising an "increasingly large portion" of consumer purchases each year does not significantly affect the argument. It is important to realize that (E) does not necessarily mean direct-mail advertisements are taking business from stores. Whether they make up a large or small portion of consumer purchases does not change how direct-mail advertisements impact the environment in this case.
Does that make sense? Please let us know if you have any other questions and best of luck with your studies!