Retarding levain

Hello, I've been making about 10 loaves of sourdough a week since the pandemic.  I usually bake 2 loaves on a given day as I always make make enough dough for 2 loaves.  My fridge is an integral part of the process as I may need to push baking to the next day because of less demand from friends or family.

So everything goes in the fridge, dough, shaped loaves, levain. My starter sits out all the time and is fed once daily. What I've noticed is that dough will knead far quicker with a cold retarted levain.  Kneading is reduced by about 50 %, and I'm curious as to why?

I use a large qty of levain in my dough . For 2 loaves my dough will be about 2300g and 760g of that will come from levain.  At bedtime I mix up about 100g of levain 100% hydration.  About 10 hrs later I add another 330g of water and 330g of flour. This sits on my counter for about 8 hrs. Then it is put in the fridge for about 30 hrs, I then take it out and it sits on the counter while dough autolyses.