Seriously? Enemies spawn in dark places, especially caves. You have to venture out to get better supplies, so you'll have to encounter monsters. Not to mention, your swords, shields, and tools will eventually break, and you'll have to craft some new ones, sometimes in the middle of a monster raid. Going deep into caves, REAL deep caves always reveals monsters that are trying their hardest to kill you as caves are dark places, especially since things like torches are not infinite.