Because that's how the update process was designed[1] - while it's not
stated explicitly, the rules imply a continuous delivery-style development
model - and it's good to have new features and bugfixes in existing
images. We used to do this even in our production images (starting from
3.11) up until 4.2 or so, when something broke horribly in the update
process.
Normally you should be (or should have been) able to update a 3.11
closure? image to 4.6. Since the update process doesn't have the Spur
bootstrap, the process broke at that point, but one should be able to
update an 5.0 image to the current 5.1 (alpha).
Let me reverse your question: why would you want to backport anything when
you can just get all the updates from the Trunk?
Levente
[1]
https://squeakboard.wordpress.com/2009/07/02/a-new-community-development-model/On Thu, 19 Nov 2015, marcel.taeumel wrote: