Returning Rate vs. Repurchase Rate

The answer is - one is a non cumulative metric and one is a cumulative metric.

Returning Customers by Cohort vs Repurchase Rate Report

Returning Customers by Cohort is not a cumulative graph.

Customers Returning Rate is looking at that amount of customers each month that come back.
Returning Customers is showing you the amount each month individually - not cumulatively.
t is looking at the activity in each month after the initial purchase. This helps you know when to remarket to customers to get them to come back and buy again.

Repurchase Rate is cumulative, so it tells you when and how much of each cohort has repurchased and the number grows as time goes on. Each customer is counted once. It looks at how many from the entire cohort - cumulatively have come back at by that time.

Repurchase Rate - tells you when the customers that you acquired come back and repurchase. What % of the customers you acquired come back and repurchase.