Well, one of the big upside of the modern smart vacuums is you can see the map it built, set up rooms or zones, do a virtual cleaning, etc... This (1) definitely requires some connectivity, and (2) has to go via central server if the phone is not on same subnet.
Sadly, because of (2), most (all?) companies don't bother with local connectivity at all. Much easier to debug one codepath (via remote server) rather than two (remote server and direct connection).
So yeah, if you are worried about device being remote controlled by its manufacturer, don't buy devices which say "Can be remote controlled" right on the box. But of course then you are back to ancient tech, setting physical virtual wall devices or bounding the clean area with overturned chairs.
This is when you only want to clean only left half of the room, for example. In the old robotics vacuums, your choices were either enough physical "virtual wall" units (those little stubby boxes you place on the floor) or physically fencing it, with overturned chairs or boxes or something.
With the smart vacuums, you get the nifty map and you can draw the lines/boxes around the area you want cleaned. Very convenient, but naturally requires some sort of device with a screen (to show map) and position input (to draw the boundaries), like a phone.
They could, but it'd still be two codepaths to debug and test - via central server and via bluetooth. So the difference would be even greater, with the benefits unclear - the amount of people who genuinely care about fully offline vacuum is pretty low.
Sadly, because of (2), most (all?) companies don't bother with local connectivity at all. Much easier to debug one codepath (via remote server) rather than two (remote server and direct connection).
So yeah, if you are worried about device being remote controlled by its manufacturer, don't buy devices which say "Can be remote controlled" right on the box. But of course then you are back to ancient tech, setting physical virtual wall devices or bounding the clean area with overturned chairs.