Fergie's new song MILF$ together with Kim Kardashian is a pop song as so many pop songs already.
But that is not a bad thing if you want to make money.
Pop songs have become more and more general over the years and that's not all due to the artists.
We look for and buy more generic songs too so we keep this cycle going.
Music artists have used more formulas to make music that people like and if a formula works there is no reason to do something else. It are the hits that brig the money in so you are better of making a safe bet then taking risks.
Zipfs law states that the probability of occurrence of words (or other items) starts high and tapers off. Thus, a few occur very often while many others occur rarely.
When formulas are used in lyrics the fewer and fewer words are used.
So it comes down to algorithms in the end.
Some other reasons why pop music could sounds more and more the same is because the number of good musicians and producers goes down and the number of artists they produce music for goes up.
The musicians also tend to learn to make about the same music and the more same music is made the more of the same musicians seem to be needed.
In other words: because the same people make it.
Experimentation is pushed to the margins and algorithms and formulas of success take over.
Have a great day.