It seems like this is essentially the same technology, but they use the "needs to follow a bike" property to deal with the fact that your proposed AI trailer likely wouldn't be street legal, and also as an easy way to deter vandalism or theft.
I see this statement all the time (that legal issues are holding AI back) but I'm pretty sure the legal issues could be fixed pretty quickly if there actually were self driving things.
In this case, if you look at the videos it doesn't look like this trailer is doing anything smart at all, it just accelerates/breaks when you pull/push on the draw bar.
Seems like a smart solution to the problem "I want to transport stuff, but bike trailers are too heavy"
Bike infrastructure is underdeveloped. Car infrastructure is not, and cars are good at cargo. Shifting cargo-hauling duty onto bike infrastructure is a great way to put bike infrastructure overcapacity, but not a great way to haul cargo. We should reserve bike infrastructure for people, because getting people out of cars and onto bikes is where the magic happens. Turning bikes into small cars -- which is where this idea is clearly headed -- is gross.
On top of this they may be wishing to get stuff to/from places that aren't very accessible by car, and additionally rental car prices are heavily determined by the price of the vehicle, the operating costs, and maintenance. The numbers on something like this are much lower than on a van.