Why do people not create space for others to sit on the subway?

I’ve lived in NYC for 10 years and have noticed an uptick in this in the past few – though maybe it’s because my commute has switched to the A line and I wasn’t taking that train before.

I’ll regularly see people on both my morning and evening commutes, prob are 80% men but plenty of women too, intentionally making it difficult for a third person to sit on a subway bench that is meant to accommodate three people. What is the mentality of people who do this?

I often ask them to create space but not if the person looks like they might react angrily.

Does anyone know people who act like this and can you explain their thinking to me? I am TRULY curious.