It's more that a typical parent has not thought of the need to have a baby monitor, until they have a baby (in which case, they're too busy to build out their own baby monitor stack).

Pay money to solve a problem and time-save as a parent is a valid business idea/strategy. The externalities that the parents might suffer if these businesses do not completely adhere to good security practices don't seem to come back to bite them (and most parents get lucky and not have any bad consequences - yet).