How does your organisation and team balance PR comments demanding changes and dev time?

Here, while fixing PR comments we sometimes end up wasting as much time as we took in actually developing the feature... As a result, almost every major user story overshoots the estimation and almost every sprint gets delayed.

Yes, to each his own; but talking in general, why do you think this time wasting happens?
Do you think that happens because some of us are not as experienced as the others, the existing code not being up to the mark giving a bad example, or just a skewed review process?