You are kind of missing the whole point of Random Encounters. It is about variety. You know how variety is the spice of life. Having Random Encounters allows players to go up against more of a variety of enemies. It also provides greater replayability combat wise for the game as a whole.
During one playthrough, I might fight a pack of wolves near Moon Haven. Next playthrough, I might fight nothing near moonhaven, but I fight a giant toad at the bog. Then during that same playthrough I fight stirges also in the bog. Next playthrough I don't fight any of those, but I fight boggles or maybe bandits on the road.
Random Encounters allows things to be mixed up and it makes the world feel more alive. I take a long rest, I get up, and I might face something new that day that I never fought before instead of having an empty world with no enemies to fight once I've cleared a certain area out no matter how many times I've gone to bed.
