I suspect there are many factors but thinking of "pop" songs, I have no doubt that the versatility of the English language is one of them. Most mainstream languages have "superior institutions" that govern accented syllables, length of vowels etc. while in English you can get away with murder or even invent your own synonyms, add doowop, say is not, ´s not, isn´t or even change the rhyme by saying "ain´t". Then there are phrasal verbs whereby by changing a preposition you can give an entirely different meaning e.g give in, up, off, out, away or over in other words it´s easy to make the words fit the beat or vice-versa.