Explanation

Wildflowers don't propagate under cultivation and hence are plundered from the wild.
Articles in Magazine often spur sales of the plants they describe, particularly among people new to gardening.

Aim - To halve the plundering of native plant populations
Plan - Don't print articles on wildflower
(Since it is a new plan, the assumption is that till now the magazine was printing articles on wildflowers. Hence not printing articles may reduce the demand)

One of the options needs to describe why the plan may not lead to the aim.

(A) When people new to gardening buy plants, they often fail to take adequate care of the plants that they buy and become discouraged from buying those varieties again.

If people new to gardening have bought the plants once, the plundering is done. Even if they do not buy again, there will be more "new" people who will buy. Hence curbing the publication of articles may reduce the number of "new people" who buy wildflowers. It doesn't explain why the plan MAY NOT lead to the aim. Hence not the answer.

(B) Plant sellers who sell rare wildflowers have no reasonably inexpensive alternate way to offer their wares directly to new gardens.

If anything, it strengthens the plan. The sellers do not have any other inexpensive way to reach out to people new to gardening. So if the articles are stopped, possibly the demand of wildflowers will reduce and hence the aim will be fulfilled.

(C) The demand for rare wildflowers rarely exceeds the number of such plants that can be collected in the wild by plant sellers.

We want to REDUCE the demand so that plundering from the wild REDUCES from current numbers. Information in (C) is irrelevant to our plan.

(D) The propagation of rare wildflowers often depends on the plant's interaction with other organisms in their environment such as plants that create suitable soil conditions or insects and birds that disperse seeds.

(E) Revenues from sales of plants collected in the wild are supporting the discovery of new low-cost techniques enabling rare wildflowers to be readily propagated in nurseries.
Revenues from sales of wild plants are supporting the discovery of tech to grow wildflowers in nurseries. If the revenues reduce, the technology may not get developed and the plundering may continue. The current plundering may actually lead to reduced plundering in the future so the plan of not printing articles may actually work against the aim.

Answer (E)