It comes down to the type of guy mark is. He thinks he is this lads lad, alpha male and the ultimate man that every guy wants to be. A part of that mindset is being able to have kids etc, a legacy and heirs. A real man will impregnate his wife (that's the style of thinking, not saying it's correct). There are many guys like this.
But for Mark to be cock blocked by his own wife, or maybe to not be able to produce kids himself, that's a massive dent to his ego and image. But there would also be an element of karma in that.