Christian churches have also changed teachings (usury, slavery, geocentrism, religious liberty) and call it development or better understanding. What makes the Witness pattern different?

Specificity and consequence. The Watchtower set dates for the end (1914, 1925, 1975) as authoritative teaching, members made life decisions on them, and the failures were reframed as new light without acknowledgment of error, while members who questioned were disciplined. The 1975 case is the clearest: the expectation was built in print through the early 1970s, and the Watchtower’s own 1980 statement conceded that mistakes had been made, which is the fairest source to cite. Christian doctrinal development, whatever its problems, did not involve repeated failed date predictions presented as divinely guided.