Like why did protestantism spread so wide,became politically backed by nobles and church and last to this day while previous heresies like the lollards,the fraticelli,the bogomilists,the cathar,the waldensians and the hussites?
Why did these heresies fail and became footnotes in history but protestantism(both luteranism and reformed branches) rose to become so important?
The invention of the printing press allowed Luther's writings (and those of the other Reformers) to be disseminated way more widely than was previously possible.
It also allowed for the dissemination of translations of the Bible into German, English, Dutch and so on - that is, languages ordinary people spoke. Before that they were all in Latin and not available for home use, unless you were rich enough to afford a handmade one. So for the first time people could compare the teachings of the Roman Catholic Church to the biblical text.