High activity means most techniques are being fired instinctively; there is little time to think. Your success rate will depend on how much you have trained your body to react instinctively. The more you spar, the more instinctively you will fight. Low activity gives you lots of time to think, usually too much time. When given more time, you tend to think about what to try next instead of instinctively firing into openings with whatever is available at the time.
If you always sit back and avoid or block, you will not score; you only score if you attack. You could be the best blocker in the world but never win a match if you do not attack. Blocking skills may give you time to rest, but you must be aware of the remaining time in a round so do you will not wait too long and end up short on points.
If you have ever been running and decided to walk a while and then start running again, you know how difficult it is to get started running again. If you take a break in round, you will probably find the time expires before you can get going again.