You can look at this way of thinking as a social convention. Japanese people often care about signaling respect with language. Someone who direct speaks about the mental state of another can be seen as presumtious.

High status people in any social circle can influence it's social customs. If people get put down for guessing other other's mental states wrong without using qualifiers they are likely to use qualifiers the next time.

If you actually want to do this, E-Prime is an interesting. E-Prime calls for tabooing to be.

I meet a few people in NLP circles that valued to communicate in E-Prime.