I'm going to mostly agree with Corri here. For some reason I am the kind of woman with whom many other women feel comfortable talking about sexual issues so I am basing my advice on over 25 years of anecdote and gossip-LOL. Many, many, many women are uncomfortable with the thought of what it would be like for their partner to interact directly with their genitals. It makes them intensely self-conscious to think about the smell, taste, general "ickiness". This self-consciousness takes them out of the moment and turns them off. It has nothing to do with whether the process actually feels good or arousing.
IMO, it is a sign of sexual immaturity. When I was 16, I would estimate that more than 50% of my peers has issues along these lines. Now that I'm 41, I would say that it's down to less than 20% of my peers who are at all concerned. IMO, the best way to deal with this issue is to make it VERY clear how much YOU like to do it. This might not be clear to your wife at all. She might think that this is just what you are doing to pleasure her. So (Regretably, I find myself having to use the vernacular of the junior high male here) you need to let her know you're thinking "apple pie" not "tuna".
"Tell me, what is it you plan to do with your one wild and precious life?" - Mary Oliver
