Probably because every "alternate" path would usually be a dead end with a dinky ahh potion or straigjt up vendor trash for a reward.

No extra bosses, no hidden objectives that gives extra rewards when fulfilled (gil, minions, orchestrion rolls, glamours, something), is it any wonder players started taking the path of least resistance? If anyone is to blame, it's SE being SE and throwing the baby out with the bath water instead of finding a way to feasibly accomodate both players that are willing to explore the dungeon they're in, and the ones trying to set an any% world record speedrun in Sastasha.