Indeed it isn't easy, but for car software, why couldn't you do the software upgrade offline, while at the mechanic, or via a USB drive with a signed installer, or via a phone app plugged into a USB port in the car? For a basic car there really isn't a need to be always online.

My car just has a bluetooth stereo, and it isn't very old. Yeah it is a basic model, but I really don't need or want connectivity in it. The one argument I could see would be showing maps, but I need offline maps anyways since I often lack any sort of mobile phone connection where I'm going. And you can update maps on a monthly basis (mobile phone app over USB while parked at home would work perfectly for this). Currently I just run OsmAnd on my phone with openstreetmap data downloaded in advance. Realtime traffic information perhaps could be an argument, but again, better to distribute that via FM radio that has better coverage (or even AM radio in some parts of US as I understand it).

And cars might be the odd one out. There really is no excuse for exposing washing machines and other applicances online. Especially since they are likely to last for a lot longer than the software will be supported. The fridge and freezer at my parents is around 20 years at this point for example. My washing machine is over 10 and going strong. I doubt they would get software security support for that long.