I'm very familiar with homeassistant, been using it for ~5-6 years. First primarily z-wave but now primarily zigbee with a tiny bit of wifi-backed matter mixed in.

That's a lot of work to replace the sensors that are built into the fridge. 2 temp sensors for the fridge and freezer separately (I'm still not convinced I wouldn't have issues with the connection being unreliable), a power clamp (you probably don't want to use a plug since the relays fail open), 2 door sensors, and a fair bit of automation to get notified, not to mention you've now added a maintenance task for all those batteries. Especially when the alternative is to connect it to the internet and you're done. I do connect my homeassistant install to their cloud service so I can get long term tracking and whatnot but the part I need is done with just the internet connection.

Why would I risk the security of my network by giving Samsung or GE or LG a backdoor into my network

That's just it, with either client isolation or a dedicated and isolated IoT SSID (nearly all modern home routers have one of these) they're not actually on your network and can't communicate with any of your other devices, only the internet. I've been building enterprise networks for ~20 years now and this is how it's handled at that level and should be more than enough for a home network.

I do 100% agree for cameras though, that's all local or not at all.