The exact cause of SIDS is unknown.[7] The requirement of a combination of factors including a specific underlying susceptibility, a specific time in development, and an environmental stressor has been proposed.[4][7] These environmental stressors may include sleeping on the stomach or side, overheating, and exposure to tobacco smoke.[7] Accidental suffocation from bed sharing (also known as co-sleeping) or soft objects may also play a role.[4][8] Another risk factor is being born before 37 weeks of gestation.[1] Between 1% and 5% of SIDS cases are estimated to be misidentified infanticides caused by intentional suffocation.[9][10] SIDS makes up about 80% of sudden and unexpected infant deaths (SUIDs).[4] The other 20% of cases are often caused by infections, genetic disorders, and heart problems.[4]

• Wikipedia, emphasis mine

Anon is insinuating that this is used as a cover-up or euphemism for mothers killing their infants intentionally, but that's only estimated to be 5% of cases at most, and those only because it couldn't be correctly determined as murder. The fact that it requires an autopsy first means presumably investigators try to find a better explanation before resorting to SIDS as a fallback.

It does seem strange to have a catch-all condition for a pattern of unexplained deaths that have a lot of things in common, but it seems like it's generally due to infants being accidentally put in a situation where they suffocate or asphyxiate in their sleep. Some situations like sharing a bed or exposing them to tobacco smoke do sound like the parents deserve some responsibility for negligence however.

Actually, I read further and it specifically says that it is a diagnosis of exclusion (meaning it's used as a default after failing to find a better diagnosis) and that suffocation and neglect can qualify.