It’s not intentional in the sense that mirrors are now un-encouraged or that the Infrastructure project would prefer them not to be made. But time has not been spent on updating mirror guidance or maintaining mirrorlists. I think it would be fine to create a repository mirroring page in the ROS 2 documentation.
packages.ros.org is distributed by OSUOSL’s FTP network which has three hosts, all in the US.
The TGC has discussed mirroring a number of times and I’ve taken those discussions back to the Infrastructure PMC.
The focus of these conversations was less about the apt / rpm repositories, which have years of standardized practice*, but about providing integrity checking mechanisms for mirrors of other project resources such as the rosdep database, rosdistro database, and ROS 2 documentation site.
On our backlog is to document how the Infrastructure project would recommend mirroring our own infrastructure. And using the gaps in that story to drive small features in that direction, such as providing integrity information for ROS 2 documentation that does not require building it from source.
If I can self-grade, the project does a fairly good job of making all the pieces avaiable to be mirrored offline. But what pieces are needed for which workflows and how to put all of it together is not widely understood and there are a limited few who could get it right in under 10 tries (I think it would take me at least that many).
* For example, apt-mirror can be used to create mirrors of the official repositories that preserve metadata signatures.