We knew one of our champions would ask this. 🙂
We have just completed a big upgrade of the mail engine system. Short URLs are about to launch. Plus, it gives us a bunch of new capabilities in the future like email scripting, long term throttling and more.
The Outlook plugin had several limitations that were causing us headaches. We upgraded those to prepare for the future this new mail engine gives us. The preview step has more control than the main window to check if there is internet access and do certain logic on the links and potentially tokens (future).
Additionally, there were special technical circumstances that forced us to take the approach we did. I can't discuss those, unfortunately, but this was the most elegant solution we could conceive.
I know it has limited value to the user and requires the extra click, but given all of the factors, it was a choice we had to make. I know you want more detail, but rest assured, we are trying to make the best experience possible given the technical realities.