The tops don't pop up on their own because of the springs, they catch wind, bump etc. The latches have never "held the top down" they just keep it from starting it's journey up. Latching the top, inside or out simply prevents the top from going up.
And the whole "lets put seatbelts as a backup on the top" is (in my opinion) stupid American oversensitivity to being sued. Yes you might die if the top latches fail, the top separates from the van in a rollover and you are thus ejected because you were not wearing a seatbelt yourself. The fallacy is the person not wearing the seatbelt is not at fault, but the top failure.
Perhaps manufacturers should add seatbelt retainers on doors, as I've known a door to fly open in a rollover and eject a seatbeltless passenger. Surely the door coming open was to blame, we should add back up safety to keep the doors closed at all times. Add Nascar Mesh over the windows, or keep them from rolling down in the first place.
Now you get in your van and don't bother to attach the seatbelt backup for the top, don't buckle the belt retaining the doors and fail to buckle the mesh in place over the window because it's too much trouble- just like putting on the seatbelt was in the first place.
Sportsmobile added the top seatbelts in a kneejerk to a potential lawsuit issue raised in a case. Before calling for extra safety from all top manufacturers, remember that they're just bolted to the existing structure and have never been tested in a crash. The SMB structure is designed to be stronger than the roof but not-necessarily to have a bolt hole drilled and a seatbelt attached under load in a wreck- and they'll do nothing if the person not bothering to buckle themselves in doesn't bother to buckle the top either.
Apologies for ranting, but this really bothers me. I could go on for an hour about how the US mandated saftey switch in tractor seats actually makes the whole system LESS safe. Adding seatbelts all over everything doesn't help if the user won't buckle up in the first place.