They possibly cannot contain the sudden emotion they felt. This could happen to those who are really in need and obsessed of money. There might also be other complications they have aside from being shocked. A sudden emotion can trigger the complications you truly have, they are just not aware of it.
Not sure if those guys had some other disease as well and that has also affected with this shocking news resulting into the heart attack easily. Because there is a difference between a pleasant surprising shock and the sad shock. This is a good surprise where you have won it and no other way around of losing it. But results in a death which is quite shocking as for the point they might be a waiting in life happens and you cannot enjoy it anymore.