I honestly don't think this is that big of a deal. There is a certain amount of force that needs to hold the door closed to get a good seal. With a mechanical latch, that force has to be applied by the user one way or another. There are several ways to solve this problem. You can mount the microwave in a fixed position, such as an under counter unit. You can push it up against a wall. You can just push fast enough that the inertia holds it in place (this works for me with most microwaves I have tried).
Alternately, you can just add weight. Sure, the manufacturer could do that, but that is the worst possible solution. It means I have to pay for transporting a bunch of ballast halfway around the world. Plus it makes it harder for me to load into my car, unbox, and lift it onto the countertop. It is even more inconvenient if you move regularly. I would much rather just set something heavy on top of the microwave myself after it is installed if I need it.