Why not present perfect in "Nobody told me"

The fact that song lyrics don't always use proper grammar is part of this - artistic license with the language.

However, the bigger part is that while English has incredibly over complicated grammar and syntax, it's also readily understood when most of the rules are thrown out the window.

I actually wrote my thesis on this topic, and it's pretty interesting.

English tends to evolve more quickly than most other modern languages, in part because its used by so many non-native speakers as a common tongue. Even still, an American, a Brit, and an Australian all natively speak English, and we all typically understand one another, but we use considerably different methods of speech and break the "rules" in different ways.

The short version is this: knowing the grammar and syntax is important, but you're likely to find that almost nobody actually uses them all all of the time. Not even writers or professors or English majors. :)

As ESL learners we are told that in the presence of a negation present perfect should be used. The reason that is usually given is that simple past is only acceptable when you can pin a specific point of time to the event in question, which is not possible in presence of a negation simply because the event has never happened.

Regardless of where you were "told" about this preposterous lie, you're wrong. The very existence of auxiliary verb contractions such as wasn't, weren't and didn't clearly shows that you can negate the simple past form of the verb.

Moreover, your example is not even verbal negation. The negator nobody is the subject of the sentence.