Almost in perfect correlation as one by one pre-existing condition limits were legislatively banned over the years. And ACA eliminated almost all remaining pre-existing conditions, so of course it drove insurance costs and pricing sky high.
If pre-existing conditions were the primary cause for premium increases, the ACA's one-fell-swoop removal of them would've had far more significant impact on that chart.
Limits on pre-existing conditions mainly affect individual policy pricing, corporate health insurance are already pooled and because of that always had fewer pre-existing condition limits.