For example, how exactly do you catch videos using copyrighted material and deal with disputes when thousands of hours of video are uploaded every hour? Doing this manually is likely infeasible. But algorithms are error-prone, as YouTube exemplifies very well. Or how exactly do you stand up to these massive billion-dollar media companies without going bankrupt during your first court case? Which (I think) is why YouTube currently simply goes along with whatever these companies demand.
Criticizing YouTube is easy. What is hard is coming up with better solutions that could actually be implemented in whatever YouTube could potentially be replaced with.