Paul told Timothy that from a child he had known the holy scriptures (1 Tim 3:15). God wrote scripture so that people could understand it, so it isn't God and it isn't the Bible that people don't understand it. What is it? What happens? Many things.
Men teach false doctrine. They conform scripture to their teachings. People might not get the Bible right because they have been taught something false by false teachers. Their misinterpretations of scripture have been taught to them. That's why they misinterpret it. You've heard Jehovah's Witnesses' take on John 1:1. That's what I'm talking about. They didn't come to that position on their own -- they were taught it by false teachers.
Roman Catholicism kept homogeneity through police power. You had two options: conform or suffer. You didn't have the Bible and your doctrine was what the church told you. Roman Catholicism wouldn't trust people to study the Bible on their own. They were wrong to keep people away from scripture, but they were right about the multiplication of misinterpretation from people with the Bible on their own.
Also men come to scripture with presuppositions. They might arise from popular teachers. They conform scripture to their presupposed positions, ones that might conform to personal freedoms or conventional wisdom.
Scripture is its meaning. Scripture is what it says. The Bible isn't a vessel into which we can pour what we want it to teach or say. It isn't God's Word when it is just what you want it to say.
Plain sense of scripture says God preserved every Word for every generation of believer, that is, He preserved it for His church like He said He would. You read passages that teach preservation of scripture either explicitly or implicitly and you get a very particular understanding. It's clear. It's also what people have believed. They conformed their publication of the text to their biblical presuppositions.
In the nineteenth century, professors met their inference of manuscript evidence. They did not refer to passages on preservation and historical beliefs. They acted on their uncertainty. Later men, who professed to be Christian, tried to adapt those passages and those teachings to their presumption of reality. Scripture was not their reality. They relied on their observation and experience. Textual criticism drew from the wells of infidelity. Professing believers came along later to conform their interpretation of preservation passages to this infidelity.
False doctrine and misinterpretation of scripture often come from the pursuit of reconciling the plain sense of a passage with a popular notion. This is not living by faith. It doesn't please God. It perverts the meaning of the Bible.