Comment 1 for bug 1272985

File -> Send To was designed specifically for nautilus-sendto, which is not merely for emailing, but also for archiving, burning to CD, and more. I agree, a dedicated "Email To" option would be nice, but we felt that would be duplicating the effort already put into nautilus-sendto and elected to take advantage of that.

As far as the steps, that's dictated by nautilus-sendto, which requires the files be prepared and ready before execution. Shotwell needs to export those photos (to commit edits and resize as the user desires), which is why that dialog comes first.