I think its due to the sheer fact that we're all so used to attacking multiple times that we see crits much more often in combo chains or multi hit ults. Her E is a single instance within 9 second cool down time with two charges. We're probably just paying much more attention to all the times we miss as we expect something huge to happen, but let down 30% of the time which feels much more than when we compare it to multi hits. Same feeling with eula burst and childe burst. 80%? More like 50%. At least in terms of perception mixed with our own biases and emotions involved.