Call centre workers can process refunds, send out replacement items and do similar routine things - and they're not that well paid. It's unlikely there will be other more profitable ways to deploy them in the company. Programmers who can make code changes to fix faults in production software cost a lot more. And there will be other departments (which make a bigger contribution to the bottom line) trying to attract your most talented people.
By design of company I mean some tech companies only employ a small number of non-programmers, so they can afford to give programmer-level salaries, benefits and working enviroment to all employees. Google could give free food / laundry / busses / nerf guns to all employees and might think the equality is culturally important. Amazon on the other hand has radically different pay/benefits/working enviroments for programmers vs call centre workers vs warehouse workers.
Wonder why Amazon doesn't seem to have those problems. To me, they have just as many, if not more products to support and yet they're still known for their exceptional customer service.