Why would this insect pest poster in Taiwan have phonetic characters (Zhuyin) on every Chinese character? In my Biology SE question Identify this large, beige or pine cone-colored squareish beetle and/or the pine cone it's on? I included a snapshot of a poster I saw when hiking. I was told that it advises that the beetle shown in the photo is a pest. I can at least recognize that it begins with what looks like "小心!" There's no date on the poster but I assume that it's modern and not a historical reproduction.

I saw this poster while hiking in Taiwan. 

I noticed that there are (almost always) a pair of phonetic characters (注音?) next to each Chinese characters. In Taiwan I see books of sutras and other prayers written this way, but I've never seen a public announcement that looked like this.

Is there any particular reason why this particular public notice would require the phonetic characters? Are they there as a courtesy? Is this considered artistic or stylized in any way? Does this make it more accessible (easier to read) or look more "official"?
Texts written for schoolchildren will be annotated with phonetic symbols. The last sentence indicates that this poster is made for schoolchildren:

如果發現了，趁著沒孵化之前通知老師來移除。
If any [eggs] are found, take the opportunity to let the teacher know, so that they can remove [the eggs] before they hatch.