Just from a numerical evaluation, I think a pump has less total parts and less moving parts than a typical sidelock ejector. Less parts and less moving parts is a huge swinger in reliability. I'm not a reliability engineer, but I've been around a lot of that kind of work in aerospace and I can pretty much say with confidence that complex machinery has much higher probability of failure than simple machinery. Quality considerations can, of course swing the reliability wildly as well. But as many of you lifelong pumpgun owners know, a 870, 12, or 37 may go thru a lifetime without a failure.
