People can satisfy their sexual urges on their own (that is, without a sexual partner) through masturbating. They cannot satisfy their hunger on their own (that, without food).
I suppose people could eat one food while looking at another kind of food pretending that the food they are eating is the one that they are watching, but where's the fun in that?
Having sex with an attractive person is an indicator of biological desirability ----- namely that another human being wants you in the way you want to be wanted due to your accomplishments or social status. Thus, people watch or read porn to satisfy their need to be accepted or to make them feel as if they are such a person with accomplishments or social status or to compensate for things not going their way in life and subsequently masturbate to such porn.
As for hunger, a better analogy for porn would be taking those kind of drugs that make you feel less hungry.
So yeah, for sex, people watch porn. For hunger, people do not compensate for their inability to eat by looking at food that they cannot have. They would probably take drugs or something. I'm not quite sure if such a thing exists, but I swear one of my grade school teachers said that there was some kind of drug that makes people stop feeling hungry.
I think a better analogy for looking at food they cannot have is looking through pictures of a lustful or romantic interest with his/her romantic partner.
This may sound like a stupid answer that is more philosophical than biological from some loser with 1 reputation. I request commentary along with any downvotes.