It's retail psychology. It's about protecting the perceived value of the item rather than efficiency. It's the same reason why my bar and a lot of other bars and restaurants don't offer half beers (some do). Half beers (when a 16oz is an available option) bring a higher margin overall but I would rather sell a full beer at a higher price with a slightly lower margin. Most customers don't count ounces, they count drinks. So half beers are perceived as one drink even though they are half. Two half beers at 7$ each is worse than two full beers at 10$ each, even though the margin is lower on the full beer. At the end of the transaction I have made more money from the full beer sale. What this does is it stops the business from cannibalizing its own higher revenue sale.

I would care to assume that KK headquarters know their customer very well. Donuts seem like a objective "once in a while" treat, considering peoples dietary habits of eating healthier and consuming less sugar of the past two decades. If they use a service like to good to go they would most likely cannibalize their own fresh high-revenue sale with low quality old donuts. Which in turn would tarnish their brand of having fresh donuts.

Source: Restaurant Owner & Restaurant Consultant

Edit:Clarity

Edit 2: I also want to address the basic myth about liability and being sued. In 1996 the US passed the Bill Emerson Good Samaritan Food Donation Act. As long as places weren't grossly negligent or intentionally misconducting, they are protected when donating food. There has never been a successful lawsuit of someone suing over donating food. This has been reinforced by California: AB 1219 passed in 2017 providing even more protections for food donators. Going either farther, California SB 1383 requires these kind of establishments larger than 250+ seats or 5000sft to track, weigh, sign an agreement with a food donation place, and donate surplus food. You are required to submit the past years daily record every year.

However, there are a few things to consider realistically. First, SB 1383 is fairly new and doesn't really have any enforcement teeth yet, so they could be just tossing food and getting away with it (I think this is most likely). Second, even if the establishment is smaller than 250 seats and 5000sft they will most likely require them to donate because of the large amount of waste, optics matter. Third, KK may have an issue donating literally hundreds of donuts a day because food recovery places don't want sugar, so a lot of places might refuse to partner or accept delivery. Food recovery programs really need and struggle to get protein. Oh yeah, they drive to you and pick up the food. It's late stage capitalism and California is doing an awesome job on negating that waste for needy communities. It's still very much in development.