Picture an invisible grid over the the screen. Now imagine that you can only walk on the lines within that grid and you have an idea of how limited movement is. This makes walking from point A to point B rather difficult. Especially when you have objects to move around or monsters to avoid. Heading though doors can become a Herculean task if it isn't wide enough.
Speed can play a factor as well.
Different creatures and characters do move at different speeds. There are some monsters one simply cannot outrun. Others are relatively simple. One of the most invaluable spells in the game increases ones speed. Unfortunately, there is no pathfinding ability to just double click where you want to go and have your character walk there.