Don't you usually want lifesaving devices to have simple designs? For example, scuba breathing regulators are famously reliable in part because there's very little to them. Same goes for the AK-47, though I suppose I'm getting off the "lifesaving" track now...
False activations of things like alarms are dangerous because it conditions people to ignore the alarm or react slowly.
Look at that circuit board for gods sake, that's probably 6+ layers and apparently required custom gaskets around crucial components. If you consider the device as a whole, it is not simple at all.
That's kind of the crucial point, too. A smoke alarm can only be considered simple when everything on the path from smoke detector to alarm is simple, and that's not the case here. Which makes this seem like a case of not getting the basics right.