Answer:
Um maybe because he is a cartoon character aimed at children not zoologists
Yes it is aimed at children, however; the reasoning behind the naming is a little more complex. When a voice artist learns their talent, one of the things they learn is that certain sounds are more remembered than others. This is an example of that same characteristic. The name Donald and the term Duck are both words which start with a consonant followed directly by a vowel. We learn in English grammar that a consonant followed by a vowel flows out, verbally, easier than words which have more than one consonant next to each other. Therefore, it follows; that Donald Duck flows better than Donald Drake. This also works for the ear. The words Donald Duck are easier on the ear (less harsh sounding) than Donald Drake. Therefore the brain picks up on these words easier and tends to remember them better as well. Corrections to this paragraph are greatly accepted. If there are any resources available, it would help. I am quoting myself as I remember reading it while studying grammar and voice training. If I remember incorrectly, please help correct me.