I do not see studies proving the cameras caused an increase in accidents only that accidents increased at intersections after cameras installed. Cameras are typically installed at intersections prone to accidents. There is no way to know if accidents would or would not have increased at those intersections if cameras had not been installed.
This is a quote from of of the linked studies "proving" cameras increase accidents.
While this study incorporated many advances in methodology over previous studies, additional work remains to be done. Because accident studies rarely use a true experimental design and data are not perfectly observable, additional careful study of RLCs is warranted to verify our results.