This statement is a little confusing to me. Because not every quest is given like this. Not only that but you can skip steps in the quest process if you happen to stumble across the monster or a future part of the object while other exploring.Quest design is incredibly copy paste, the entire monster hunt side activity is 90% the exact same quest (check board, talk to NPC, go to area 1, active red vision trail, follow trail, loot quest item, go back to NPC, go to area 2, fight generic monster) and most other side quest are also very repetitive.
Furthermore most games only have one or two ways of giving the player quests. Much less having only a small number of quest types within the game. Usually because that's just how that given game is designed.
You mention WoW, but all of wow's quests are given 1 of 2 ways. Either you talk to an NPC, or a monster drops an item that starts a quest. Then every quest falls into three types, go kill stuff, go gather stuff, go escort some asshole while he gathers stuff and you kill stuff. The reason for this is so that every quest feeds into the gameplay loop.
The Witcher is the same thing. Geralt is a Witcher so most quests are going to be Witchery things. Investigate a monster attack, hunt the monster, kill the monster, repeat.