Cinnamon Bourbon Raisin Sourdough

Someone needs to explain to me why my doughs with only fruit in them move so slowly and feel super heavy? I can add the same quantity of porridge in a similar recipe and my bulk is done within a few hours. Whenever I use fruit, the dough takes forever to rise and feels really heavy. I decided not to rush this one and give it all the time it wanted. It did feel a lot better during shaping but once again, they are not light and airy loaves after baking.
Recipe
Makes 3 loaves
Add-ins
220 g sultana raisins