First, you seem to be seeing these devices as replacements for proper parenting. I'm not so sure that's what they're for. They're really just an improved version of the baby monitor, which is in turn an improved version of sleeping near the baby's room and praying you'll wake up when something's wrong. That's all. There are some bells, whistles, statistics and graphs, but it's just a fancy baby monitor, in the same way the Nest is just a fancy thermostat.
Second, there's quite a bit of literal survivorship bias in your comment. Most people you've met haven't unexpectedly kicked the bucket when they were a few months old, but that you don't know any doesn't mean it doesn't happen. The good news is that less babies die nowadays than there used to - the infant mortality rate used to be six times as high back in the fifties. It's still too high, though, which is why we do need devices like these.
They look like cutesy cuddly turtles and nice onesies, but they're medical devices. They assist parents in the same way a baby monitor assists parents. Help the parents, help the baby, reduce the statistic. Is the decline in infant mortality only because of the baby monitor? No. But if you, like me, see it as a medical device, I hope you'll agree that everyone should get one, not only sad, lazy people that suck at parenting.
Humans have grown to adulthood for hundreds of thousands of years without heart monitors, thermometers, incubators, X-ray machines, CAT scanners, dyalisis machines and all that as well - and I don't see you suggesting to do without those.