Because SP's are so unfaithful and untrue.
Don't mix up immaturity and general bad behavior with type. Type isn't supposed to shed light on that. That is up to the individual. Every single type is just as likely as the next to cheat. Simply because SPs and ESFPs are seen as those who want to have many "experiences", that does not mean they are more likely to cheat.
Why people choose to cheat is subjective and different for every individual and still should not be related to type. "Have you ever cheated?" "Why have you cheated?" are better questions in the overall realm of this topic. As the way you worded it still has something to do with type and I don't think the two are related.As @WildWinds wrote, infidelity is related to dishonesty. A more valid and interesting question, therefore, would be why different personality types cheat. The reason an ESFP would put forward would most likely look very different from the rationalizations of a cheating INTP, for example.
I hesitated about INFP because most have really strong natural moral codes. I agree they would definitely have to be in an unhealthy state.Hmmh, I bet Perceivers will bash me for this but judging from my own experience and what I've concluded, I think P types are MORE likely to cheat than J types. I'm not saying that all P types cheat or that all J types don't. However, from what I've read of the types, most J types tend to be described loyal, while P types are sometimes described to "change partners frequently" and so on. But obviously everyone is an individual.
Also, I know two INFP persons who have cheated numerous times, therefore I am a little prejudiced in that way. Then again, they were both simply very unhealthy individuals.
There's also a difference between physical and emotional cheating. Usually people do it in the physical sense. But I know I would absolutely never ever do such. I don't think any INFJ would. There's actually a thread on cheating and INFJs in the INFJ subforum. Nevertheless, I'd like to think that we INFJs are the least likely to cheat. At least in the physical sense...
But yet again, we're all different.
Not all feelers get attached to the person, but to their own selfish feelings. I've witnessed many feelers who can easily make excuses to justify irresponsible actions. I've seen them even lie to themselves that they did anything wrong.Sometimes it can come down to sheer luck I think. Some people are lucky to find their 'perfect match' quite early on in their life, some others, not so lucky.
I would say, XXTX's are able to distance themselves from sex much more than F's, as in T's can think of sex as just sex so I would say they are more likely to sexually cheat on their spouse. Whereas XXFX's are more likely to become attatched to someone if they make a good offer at the right time. But not necessarily sex.
I think at times different people can be right for different stages of people's lives. But I will never forgive dishonesty.