I would have to agree that the biggest reason why so many families break up because of this issue is because (like everyone has mentioned) the guy wants to save his family and achieve some sort of peace in his life.
As for the influence issue...I don't think it's so much that men are easily influenced as it is an issue of human nature. You hear something often enough from your wife or husband (i.e. "why does your mother do XYZ, we never do it that way" or "your family takes advantage of you by doing ABC") that you start to believe it...even if it's not true. And that's when the cracks start to appear. So often I've seen guys in my community who for years have been perfectly happy with their families and their way of doing things...as soon as they get married, they start getting critical of the same families who they previously had no problem with and start separating themselves from them. I've seen newly married women do this as well.
Sheyn said it best. Men (and women) need to strike a balance between the new and old families and try their best to do the right thing...instead of just walking the path of least resistance. That's the ideal though. Sometimes it's not always possible, unfortunately.