Spinning platter drives have parts that form a more relatable metaphor to humans' notions of wear and tear: skates of magnetic readers flying on a cushion of air above a rapidly rotating disc, with the gap separating a few dozen nanometers, often smaller than the process size in the controller's silicon. They have arms that can move the head over a particular disc radius, and a motor that spins the entire stack of platters. These mechanical components exhibit wear proportional to their use -- this makes intuitive sense, and is also recorded in the SMART attributes, so drives in old age and of many park cycles can be replaced preemptively before they catastrophically fail.
SSDs are missing many of the usual mechanisms that would contribute to physical wear leading to sudden catastrophic failure in advanced age. This means that irrespective of their failure rate vs. HDDs, a higher proportion of their catastrophic failures are the fault of the controller. This is discouraging: essentially, the "storage layer" is now quite reliable, so the fallibility of the human-programmed controller is brought into light.