What Do You Mean It's Not Political?/Analysis
One factor that leads to things being interpreted as political allegories is that writers read the same newspapers as the rest of us, and have opinions just like everyone else; just because a writer doesn't run for office (like Norman Mailer and Upton Sinclair did) doesn't mean he or she doesn't have political beliefs, and those beliefs often subtly (or not subtly) in the work. Another is that many politicians are buffoons, and many fictional politicians are portrayed as buffoons, and there's inevitably overlap in the buffoonery—particularly if the author has a specific pol's antics at the back of his or her mind.
Some countries also have got a tradition that intellectuals should largely discuss political issues of important historical events like World War 2 or contemporary events in fiction. Because of this, in these countries, authors of certain genres may also get the reputation of integrating political messages in their works no matter if they really did that or not.
Certain political theories and ideologies, such as various forms of Marxism, also adopt a perspective that everything is to some degree political, as the political informs and governs every aspect of our lives in some way, shape or form. According to this approach, nothing can be truly apolitical, as to be apolitical is to tacitly condone the status quo; even if you disagree with the status quo, by not speaking up against it you are essentially condoning it, since nothing's going to change.