The problem is the lack of people’s interest in deep topics,

I’m not sure about that. I think small talk serves occasions where you might want to keep it polite as deeper topics tend to become emotionally loaded disputes.

For example, going to a bubble tea shop. Usually, you don’t want to discuss the meaning of life with the shop keeper, but it may be a nice gesture to talk a bit about the small things in life. Small talk is a good way to share a pleasant conversation and appreciate each other.
Furthermore, small talk can serve as an opener to deeper topics if the occasion arises and everyone seems to be in the mood for such deeper topics.

Anyway, my wife and I are friends with the shop keeper now and we’ve talked about the weather, religions, vacations and how to raise children.