I was raised to believe in god (far from strict however), and still do, but my current beliefs are not seated specifically in any relgion.
What we believe now is never just a feature of our upbringing. It is also a feature of our experiences since then.
Someone brought up in one faith or another will continue that faith if they perceived it as a positive feature in their lives. They will reject it if they perceive it as a negative one.
And if they trust their parents, 'because my parents do' is a valid response for them, the same way we believe the statement preceeded by 'studies have shown', because that indicates that some study has been correctly performed, (assuming that we value study data over or equal to our own experience.)
No one keeps a survival mechanism that doesn't work for them.
Those who feel people follow a belief only because their parents did are missing a critical point, and devaluing the individual experience that results in the decision to continue the belief they were brought up in.
Now, do their experiences reveal the truth? Or are they wrong?
That's subject to opinion.