Most people start spamming their keys when something gets just outside of their standard comfort zone which is usually much higher than even just barely passing something. Most people don't understand that your comfort zone does not have to move at the same rate that your actual skill moves.
Most people have an instinctive response to things that feel too hard: "omg, wtf, mash!" But it's possible to push your comfort zone up high enough that you no longer feel that panicky "omg i cant read this, wat do?" kind of response. That response of trying to mash breaks your concentration. When you push your comfort zone high enough, you stop having that response.
Now, when I see a cluster of notes I know I can't hit, I have enough time to see what the cluster is, and try to figure out how to "mash" the keys in an attempt to hit as many of the notes as possible. I can only do this because I've pushed my comfort zone high enough to do it. Even if I know I can't hit something, or even completely read it, I can usually still manage to get an incomplete mental picture of what I need to do, and I can make an attempt even if I still can't play it well enough to pass.
If I played against a room of people roughly my skill level, but who haven't pushed their comfort level as high as I have, I might end up with roughly the same score on say, a level 30 o2jam chart, but I would almost definitely be able to score considerably higher on a level 90 chart.