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The case in Taiwan is extreme, as you can see from the images I posted above, there are many empty seats but the uncle die die wants to sit at the reserved seat for elderly

The old man is not wrong too.  The reserved seat is reserved for him.  The younger one should not have sat in the reserved seat in the first instance when there were empty seats elsewhere.  The old man might be thinking if he were to sit at the other empty seats,  he would reprieve other younger people from having a seat if the next station is full of waiting young passengers.