Parents who were cheated on: Why did you choose to keep your spouse's/partner's infidelity a secret from your children?

I've been seeing this a lot and I've been wondering why. It's one thing if the children, are still young children, but it seems that the children are still kept in the dark even when they become adults. The truth is important, and it's important to me, so if one of my parents cheated on the other, I would want to know because I have certain principles, and I would never want a relationship with someone who committed such a betrayal and broke the trust in the family. If we're supposed to be part of a family, then being honest and being informed about such a huge thing should be part of that. There's a saying, "I'd rather know the truth and be sad, then live a lie and smile like a fool".

I've also seen the parent that was cheated on become the villain to their children, because the children don't know the truth.

For example, if a husband cheats on his wife, and she keeps it a secret from her children and eventually leaves, the children may see their mother as the villain and as the one who "broke up the family", because in their eyes, their mother left a man who did nothing wrong. It also robs the children of being able to make an informed decision of the situation on their own, and how they want to view their father, because they don't know the truth.

There seems to be this unspoken "rule" to not tell the children when the husband cheats. I don't know if husbands do this too when the wife cheats, I've seen it mostly with mothers. The children's father don't tell them either(which is cowardly) but this also leads to the children taking the dad's side, and even holding them in high regard, thinking of them positively, when the dad was actually the one who wronged the mom. This also means that the father allows the children to believe that the mom is the villain, which is sh*tty.

Idk if this has something to do with historical context. It's like the whole, "the kids thought that grandma's marriage was so happy, but they didn't know what really happened in her marriage with grandpa", type thing. For example, grandpa cheated the entire marriage and had another family down the block type drama. This whole idea of "protecting a man's reputation" is quite old and the unspoken "rule" of keeping it a secret may take its roots from those times. If a man wants his children to think positively of him, then he shouldn't cheat. Why is there such a commitment to hiding that a man betrayed his wife and family?

To those who were cheated on and kept it a secret, what is the motivation behind not telling the children, even when they're adults? I've really been wondering about it.

Note: Excuse the "need support" tag, I was looking for "question" or "discussion" but they weren't available. It was the closest I could find. This is my first time making a reddit post, so please have some patience while I try to work this platform lol.