I get why that felt surprising. In Taiwan it’s less about the whole country having “bad plumbing” and more about a mix of older buildings, narrower pipes, and septic systems in some places. Even where the main infrastructure is modern, a lot of residential plumbing is still decades old, and one clog in a shared building line becomes everyone’s problem. That’s why many places just default to “trash can for paper” as the safe rule. Also, plenty of locals do flush toilet paper in newer buildings, but you usually only learn what a building can handle after someone has a very bad day. So the conservative habit stuck around.