This is the kind of question that can fill many books (and does). In broad strokes, Wycliffe's conclusions were considered revolutionary and didn't "happen earlier" on the same scale partly because it was a very big challenge to the social order at the time, down to the very way people thought about their own place in the world (that's in VERY broad strokes), and in short, the conditions for sweeping change to take off like that weren't right--usually, the average peasant just got along with their parishioners or they didn't, end of story, and the learned elite didn't have a reason to fix what wasn't broke. The Black Death changed all that, as I'll say below. Wycliffe himself criticized the papacy and "bloat" in the Roman Catholic Church, claiming that the church didn't have a right to the authority it used. He also pushed for a vernacular Bible, and when the idea didn't pick up steam, he did it himself.

"Orthodox" in this context just means pope-approved Catholic doctrine, theology that the majority of the clergy agreed on. Wycliffe put forward some ideology that wasn't orthodox: the idea that relics and icons should be done away with, rejection transubstatiation, and most importantly, a criticism of papal authority, just to name a few.

What happened before? On Wycliffe's part, the Black Death was a big part of it. There really isn't a way to overestimate how much it changed the scene once it swept through England. In short, think of how you might be affected by about every 1 in 3 people around you having fallen dead in recent memory. If you're an especially religious and learned person like Wycliffe, it'll have an impact on how you think about the "transient world" around you. You're alienated. You might think the world is ending (Wycliffe did). Huge population reduction meant the value of the individual shot up, and suddenly those "unwashed masses" are making demands.

Which brings us to the other very, very big thing that happened just before things "got tense" between Wycliffe and the pope: the Great Rising of 1381. Wycliffe was officially excommunicated in 1382 on the heels of the biggest peasant revolt England had ever known. The revolt was in large part motivated by taxes; the peasantry was chafing under laws that forced them to accept work for low pay, and the Poll Tax was the last straw. Worse, King Richard II's administration had no idea what to do about it--peasants rose up like an organic, unified mass almost overnight, and the administration genuinely couldn't conceive of treating with them on equal ground, that was unheard of. It scared the nobility witless. Back to Wycliffe: of the "inciters" of the revolt was a guy named John Ball, a Wycliffite preacher who gave the famous sermon line, "When Adam ploughed and Eve span, who among them was the gentleman?" To the ears of a clergy that by now owns a tremendous chunk of English land and has a monopoly on the language of "learned folk," them's fighting words. The revolt was dispersed, of course, but the damage had been done: there was a Bible in English out there, and as you can imagine, heresies conveniently start springing up left and right. Wycliffe's followers, called Lollards, get cast by the church as this great unseen threat, like a communist "red scare" in the middle ages. That's when things get ugly. A few people get burned for heresy, documents start getting screened for Lollardy, a few Lollard nobles like John Oldcastle go into open rebellion, and so on. The harsh repression was in part because King Henry IV was a usurper--he and his supporters had recently taken the throne by force for reasons that would be an entirely different thread. In short, Henry's administration had to scramble to make itself look very legitimate and very orthodox, and the faceless Lollards were a fabulous target. The Lollards were by no means organized, and a lot of religious historians will tell you not to be quick to call them precursors to the Protestant Reformation that came in the next century, but that's the gist: the world had just faced a natural disaster, and England was in a powder keg of a crisis of authority and political tension; perfect breeding ground for a heresy that says all humans are equals and should have access to the holy book.