I think of this sometimes like a roller coaster park where you pay a flat rate to get in and then ride as much as you want all day. The ideal scenario for the visitor is to go in and ride continuously, not waiting for anything. However, the ideal scenario for the park is for you to spend your whole day in queues, not taking up space on the rides, and not running around making the park feel "crowded". The equilibrium is the park studying what people's upper tolerance is for wait time and then ensuring there are just enough rides that everyone comes close to that but few exceed it.

Obviously it's not a perfect analogy, but having people wait in line on the phone does serve an important function for the CS department in the sense that it gives those folks an extended opportunity to either solve it themselves some other way, or give up. Neither of these are great for long term brand loyalty, and the cost of the added frustration is probably mostly borne by the hapless agents who do finally end up taking those calls. But from the point of view of short term bean-counters, I would guess that it's unlikely any of these dark patterns are an accident (even if they don't implement the patterns themselves, they would hire the consultant who "streamlines" the after-sales experience to optimize for cost).