A couple times a year a pre-release build will cause issues for some people and will sometimes not even restart properly. It would be a shame to show up to your TV and try to watch something and find out that your DVR had auto-updated to a broken build while you were away.
If you're actually having to hit "update", you're seeing if the update worked or not and can reach out to us if you run into problems.
We've continued to try to make improvements to the product and to TVE specifically to reduce the need to update pre-release builds, and are pushing out stable builds more frequently when the need arises to try to reduce the need for people to be feeling like they need to update to each pre-release build we push out.
All of these things are the reason why we don't have an auto-update and are unlikely to do so.