Open spaces have TOO MUCH FLEXIBILITY*. Also, there is an underground river in this cave that has some open (wider) spaces around it!
The grass clumps kind of show a path because they don't pop up around areas far from water, and the largest bodies of water are on the way to the exit. It's not a very big dungeon, anyway. Three maps, a boss chamber, and two optional maps under the main path for Moar Loot. It doesn't need a gimmick like that.
*I am kidding, it's just how I like to map.