I Do Not Understand

I know 3 couples where the husband or wife was caught cheating but they are still together. That is their choice but not the part that I don't understand. What I don't get is you know they are still cheating but they are constantly posting on facebook about how great their marriage is or how what a great husband/wife they have. It is over compensating. Why go so overboard saying how great your marriage is when everyone knows it isn't