Because of the reason you gave. A game designed for them is nearly unplayable with them turned off.Why don't you just disable them in the menu?
I was playing Gothic 3 recently(went in with incredibly low expectations) and nearly every quest that would have required some kind of intricate marker instead was designed to lead me there in some way. Either I'd find it eventually because another quest led me there, an NPC would give me directions, there would be some sort of breadcrumbs, or an NPC would escort me there. It really contrasts with games that just throw a marker on your map and expect you to run towards it.
Gothic 1&2 were even better in that way, (and far better in almost every other way too). Gothic 3 is mostly shit by comparison.
As far as TW3 goes, I played without the mini-map and had no problem finding things in 90% of the quests. You just have to pull up the map screen a lot.
In CDPR's defense, it would be prettty tough to find things from directions alone given the size of the game world.