but i think for many people a good old trailer would make more sense really.

I agree. Unless someone has room for a traditional bike and a large cargo bike, a trailer can do much of the same things, but in a smaller form factor and with far more options for flexibility (storage, cost, space, manoeuvrability, etc.).

That said, I saw a few bakfiets this past weekend with kids inside (one guy was hauling his dog), and it looked like so much fun to ride and be ridden with!