Many IoT devices, printers, and routers sold before 2019 have hardcoded or extremely weak default passwords. A 2019 working list almost always contains admin/admin , root/root , 1234 , default , password .
A passlist.txt is essentially a map of human psychology. It contains not just dictionary words, but the cultural DNA of the internet. It holds the names of pop stars, sports teams, fictional characters, and the inevitable variations created by lazy "complexity rules." When a user is forced to add a number to their password, they almost always append 1 or 19 (often a birth year) at the end.