Were there external factors, like the weakness of the Church due to unpopular policies (i.e. indulgences)? Maybe internal ones, like a more successful strategy?
More can be said, but consider
Why didn’t the Protestant Reformation happen before Martin Luther? Various people (such as Wycliffe and Hus) raised similar issues to Luther over a 100 years earlier, but they didn’t have anything like his impact. written by u/dromio05 discusses briefly why previous reformers failed and what they did.