I don't buy a U-Haul truck just for the occasion that I'm moving, am I?

In a less snarky response, in case you can downscale your primary car to be more efficient and less costly, you can save significant amounts of money. In my country, weight, size, type of drivetrain and the sticker price all determine the amount of tax you pay on the vehicle. Getting a small, light vehicle instead of a big one you need for towing can definitely make sense financially, even if you are going to tow a caravan once a year and therefore have to rent a car to do so. Of course the individual circumstances really change a lot and in general people don't do this due to convenience or the simple fact that they do this more often.

But you also missed the point of my reply. The point is that these tow bots will essentially be a second vehicle on their own. It will be expensive to buy one, it will be expensive to rent one and it will be expensive to own one. It won't make sense as a product, even if you can still use your car when you arrive at your destination. The economics won't work out, I'm pretty sure of that.