Why would this insect pest poster in Taiwan have phonetic characters (Zhuyin) on every Chinese character?

Question

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"?

Answer 1

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.

Answer 2

This is bopomofo. Taiwanese people use it instead of pinyin for transcription. They also use a bopomofo keyboard for typing on their phones.

I'm travelling in Taiwan right now and I've seen it in children's books:

and in very few other places, such as the zoo: