Not a bad practice, but costly in dev time and a trade off many aren't willing to make especially in smaller companies where mistakes aren't as costly as all that extra developer time.

Personally I do code reviews mostly to share knowledge and culture rather than looking for bugs. Occasionally a bug is found, but I don't generally have the time to review the logic, just the style.

I work for a company that averages around 50 production deployments per day for our customer-facing ERP, and we only do code reviews for new devs and changes to underlying framework changes for mostly the same reason sklivvz1971 mentions. We rollback very infrequently and a majority of our devs can deploy to prod with the push of a button as needed (this includes both application and database code). Not arguing that code review is unnecessary, just feel that with proper training and having devs with good judgement can help reduce the likely hood of breaking things when deploying small changes frequently.

Don't get me wrong, we review code. We simply don't review commits. Reviewing absolutely every commit would feel like a waste of our time and an efficiency issue. I can see where it could be useful, but in our case it's simply a solution to a problem we don't have. We can definitely live with a bug in production for 5 minutes.

As a commenter below notes, there are always two pilots in an airplane -- and that is pretty much also a trust issue -- but we don't pilot planes, we don't have actual lives depending on us.

Don't forget the role who does most of the work, the autopilot :)