The current workflow for tags requires posting, then adding tags. This is both inconvenient for the poster (more steps) and will make later tools for post review more difficult.
The line asking for tags should be something included in the question post so one post action can mean the end of the process.
Update May 2020: this is now implemented
This is a popular request and I've moved it on to [to a GitHub issue](https://github.com/topanswers/topanswers/issues/19) so work can begin. I will update the post here when it is complete.