Let's add conformity to (wrong? IMO totally) social/religious rules like "you cannot divorce". Because if your spouse passes away, either young or when it was their time so to speak, and you aren't genuinely sad, well, why were you two still together? If you spent a happy life together with someone, you should be sad even if they passed away serenely, because hey, it was the person with whom you shared and lived almost everything. If instead you were still together but actually secretly hating each other, or just because "it was always like that", well, the marriage should have not lasted til that point. If it did, it was most probably due to social rules to follow no matter what and/or patriarchy. And if it was a young person, well, even more! A young loss should generate even more grief. And the "real man" part...well, I think it explains itself.

I understand this can come off as simplifying too much but I believe it boils down to those reasons in the vast majority of cases. So, there can be exceptions of course but they are a minority.