It's because consumers have rights too. Standardising something actually fosters competition (healthy capitalism), increases profit (as standardising something often leads to lower manufacturing costs) while reducing costs for consumers (due to increased competition). It also reduces waste which is good for the environment.
> I don't see any win besides a minor convenience.
You will, when you have to buy another USB-C cable for your iDevice. I recently had to, for an iPad Air, and I was able to buy a good quality replacement USB-C cable (of similar spec) from Samsung for Rs. 750 (around $10) rather than paying Apple an exorbitant Rs. 2000 (around $20+). (Past experience with Apple cables has taught me that the higher price charged by Apple is no guarantee of better quality, and other non-Apple cables from reputed companies are often cheaper, more durable and last longer than Apple's).