At lower weights, it's easy to 'have good form'. The muscles can easily compensate for each other and one doesn't have to think too much about which muscles to contract/focus on.

As the weight increases, it requires more focus to ensure that you are keeping your form and positioning and even just to engage your muscles `in the right way`. Form becomes more important/a pre-requisite in a way that ramps up as the weight increases as mistakes become harder to correct on-the-fly. The tolerances decrease and so the technique becomes more important.