Think about the position they are in, as men. Not only do they SUSPECT they are inadequate lovers, they are absolutely correct in this suspicion and have been told this by their wives. That can't feel good regardless of whether it is the truth or not. To know that you are not even beginning to satisfy your mate has to be a serious bummer. I think the more they focus on this aspect (no matter how much I give, it is never enough for her) the more disinterested and unmotivated they become.
So if we were married to hd guys, the masturbate in front of them trick would send them through the roof because there is no way that they would be intimidated by that or have any other reaction than, Damn she is hot. Our guys on the other hand, would immediately be besieged with thoughts of "She wouldn't even want to do that if I were taking care of her" or "How often does she do that b/c I'm not satisfying her?" etc.
They don't think like HD men because we don't TREAT them like hd men! I would never fawn all over H and tell him that he just wears me out, etc, because it isn't true. I am very complimentary to him but I don't fib.
So I think that there are areas that, rather than turning him on, instead cause him to think about how he is not performing.
In addition, I think that while your H is saying that he wants more overt action, his idea of overt and seductive might be totally different than yours. To him, seduction might be talking to him, whispering in his ear, crawling across the bed towards him...as opposed to the more scary (to him) versions where you are asking for pretty technical sex moves or masturbating in front of him as a form of seduction.
Don't get me wrong..there is room in a marriage for BOTH of your preferences and you will have to negotiate that for yourselves, but I was simply answering the "why would he do that?" question.
Oh, and one more thing..I have no idea if your H is like this but mine reacts much better to me saying what I want in a 'fantasy' type setting. That is, I would tell him that I wanted to masturbate in front of him and then describe in gory detail what I would do to myself. This would get him going much faster and effectively than actually DOING it in front of him. I suppose because it allows him to perpetuate the idea that he is satisfying me...if it is just a fantasy, then it is not an ACTION that screams to him that I have a need to do this. It is just something I wanted to play around with and get him revved up with.