A smart doorbell or baby monitor gets bought, plugged in, and connected to the Wi-Fi in about ten minutes, and the password it arrived with almost never gets changed in that ten minutes. That's the whole problem in one sentence.
Why this one's different from a laptop
Watching a doorbell camera or a baby monitor remotely, from work or from another room, means the device needs to be reachable from outside your home network. That's genuinely useful. It also means the same reachability that lets you check in on things can let a stranger do the same, if the password never moved on from the factory default.
A device you can check on from anywhere is a device someone else can potentially check on from anywhere too.
The five-minute fix
Change the default password the day you set it up, not "eventually." Use something unique, not the same password as everything else in the house. If the device offers two-factor authentication, turn it on. And if you're shopping for a new one, a quick search for the model name plus "security" before you buy tells you a lot.
It's not just the camera
The same logic applies to smart speakers, smart plugs, and anything else with an app and a Wi-Fi connection. If it has a password, it's worth knowing what that password actually is.
Sfinco Guides Volume 3, Family & Home Network Protection, covers exactly this. See what's planned.