The platform trucks like you describe work well for people who are trained to use them and for others who are willing to exert the effort to think about how to use them, but I guarantee that the masses that shop at Ikea would quickly get themselves in a position in the store that they're unable to get out of, which is likely to either cause damage to merchandise as they slam into things or require significant additional help from staff.

As support, I'd like to point out the endless stream of videos showing people who cannot parallel park, despite years of experience in their cars.

Edit: I will say that there is a type of cart that I've encountered at home centers that seems to be a happy medium. It has four swiveling wheels at the corners, but then two fixed wheels in the center along the long side. These wheels sit slightly proud of the plane that the four corner wheels describe, which means that you tilt the cart slightly when using it, so that you are using the center fixed wheels all the time, but only one pair of the corner wheels. It seems to make the cart significantly more intuitive in its handling. Example