Help Me Understand This

So my wife, 39, is really cute for her age. She has nice c cup tits, good looking ass, cute smile, really sexy well maintained bush and is in pretty good shape for a woman her age. Most would consider her a milf. We go to naturist resorts or nude beaches and she frolics and interacts with others while completely naked and has a great time. We went to one resort in Mexico that was adult oriented and she entered a lingerie contest where she posed, stripped, and spread in front of a large crowd. I've got a lot of compliments regarding her, from men and women. She even prefers nudist and naturist vacation over regular ones. But, when we go to a normal beach she wears an old woman swim suit. She's completely embarrassed about her body, and says she's afraid her bush might poke out or that she wants to hide her belly (which is not even fat, just has some stretch marks).

I can't wrap my head around it.