The issue is not that the bridge will collapse (that’s entirely ridiculous considering the weight of even thousands of locks doesn’t come close to just a handful of people not to mention a car) bridges are designed to carry that much weight, it’s a non issue. No, the actual problem is that the railing will collapse as it isn’t designed to hold such weight.
If you read stories about a bridge collapse because of locks you need to read it closely. It is almost always hyperbole when what actually happened was the railings collapsed or the bridge was not maintained.
Any bridge that actually collapses from the weight of these locks was going to collapse anyway.