It takes me almost equal time to manage a Kubernetes cluster with 10 nodes as with 100 nodes. If I have to spend say 5 hours per month and with a cost of say 100 usd/hour it means it cost 500 usd/month to manage. If leaving cloud saves say 100 usd/node from 200 usd/node it means for a small company its cost would be (10100)+500=1500 usd/month which is a cost reduction of 25%. For a large company it would be greater (100100)+500=10500 which means a 47.5% savings. Do you see why the savings are greater with scale?
well bigger clusters have weird complexities and require specialized knowledge if you don't want your production to blow up every couple of months.
small clusters can be run with minimal knowledge which means the added cost is $0.