We voted in the last one for something. We still don't know what, as there is no deal agreed yet. It also seems unlikely that a deal will be agreed, especially given the makeup of our current Parliament which is simply not built to deliver Brexit.
What we've got as a result of the vote is 2 years of Parliament doing very little on anything else but Brexit. A dereliction of its day-to-day duty. That's been the main outcome of the last vote so far.
At some point in the near future we may know more about what's proposed, which is more than we know now and way more than we knew before the first vote, so another vote could be seen as reasonable, where:
* vote 1 was to kick off the process, put the day-to-day on hold and get to the point of agreeing deal/no deal/remain
* vote 2 was to choose one of those three options
Can we really trust Parliament to deliver Brexit? Whereas an AV referendum on those three options would deliver the one that most voters favoured.