In some cultures, it could create a situation where you are showing you're better than me and the person would feel humiliated. It's about the socioeconomic status[0] and how each person values that. In some countries that's valued more than other things like, say, being a kind person.

The author of this article seems to have lived in US/Canada which are very capitalist societies where people are expected to work hard and gather a lot of monetary resources. In these societies, showing you're better off than your friend might be considered a bad thing. People often hide things they bought or don't talk about that new house because it would create an awkward situation where people are comparing their socioeconomic status to others.

Is it stupid? Yes, but that's life.

0 - https://www.scientificamerican.com/article/the-psychology-of...