Why men Like to watch wife with other men?

For a variety of reasons. Some are so visually stimulated the act of seeing their wife with another it is more like a "live action porno".

There is the classic "cuckold" reationship where the male submits to his wife's desires...This usually involves a variation of the Dom / Submissive relationship.

And finally - the man may feel he is sexually inadequate and believes his wife deserves a level pleasure he cannot provide.