Witness epistemology: "I know things as a witness, not as a being pretending to omniscience. This is what I see. I do not know if it is anything more than my perception." This admirably humble and limited point of view is unpopular. Why? It just feels wrong? It doesn't lead us to seek the truths we need to survive or to do what needs to be done for others?
Those are possibilities. Another is that it may lend itself to solipsism. Solipsism is not an attractive view to most people, and things that can go down a slippery slope to solipsism may be suspect. If suspect enough, we "know" them to simply be untrue. In this case, "knowing" is a kind of shutting down of the ability to believe, to harden oneself against pathological beliefs. So to say "I know things as a witness" is to say "I know what I experience, and only that". All we need to add to that to get to solipsism is "Somehow the only things that can be are the things that are knowable", which philosophically sounds suspicious, but which we might "know" to be true, or feel a strong bias toward believing as true.
Surely, following something like "whereof one cannot speak, one must be silent", we can only talk about what we know of. Or at least, that sounds like it makes sense on some level. But then we like to make the leap that what we don't talk about, or oughtn't talk about, doesn't exist. We don't have a right to concern ourselves about it, so we should live as though (or pretend that) it doesn't exist. And so if we are fully epistemically modest, we seem to tend to have to be solipsists.