If anything you actually need more lower back strength in the front squat. Most people who are equally efficient in both movements will have a back squat that is about 120% of the front squat.
But some people have bad levers for the back squat (long limbs) without being affected as much on the front squat. I had a training partner who was about equal in both (he was a good lifter, not a beginner).
So it's either:
- You are not mechanically suited for the back squat
- You spend more time practicing the front squat
- You have relatively weak hamstrings