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.

How original were Martin Luther's 95 theses? again written by u/dromio05 talks briefly about some texts and one council.

More can definitely be said, however, to address the specifics of reform efforts (or lack there of)