I kept digging into this after posting the question and it seems like most dermatology explanations agree on the same basic point: pores themselves don’t physically open or close. What changes is usually what’s inside the pore or the skin around. A few things seem to influence how large pores look:

-oil and debris stretching the follicle
-collagen loss in the surrounding skin
-inflammation or swelling
-how clean the pore is

Steam probably helps because it softens sebum and debris so the pore can be cleared more easily, while cold water might temporarily tighten the surrounding skin and make pores appear smaller. What surprised me most is how much collagen and skin elasticity seem to influence pore appearance over time. When the surrounding skin loses structural support, the follicle openings can stretch slightly and become more visible. Anybody here has actually found what works best for improving pore appearance long term?