There’s no motivation for that, it’s just the effect when you audit segments at random, if you hold a smaller percentage of the total, the chances of your node holding a segment that is being vetted is smaller as well.
Now I believe there is already an additional audit process that audits unvetted nodes first. But since auditing a segment involves an audit on all 80 nodes holding pieces for that segment as well. Even this still audits nodes with more data more often.
If this process is implemented, it does not seem to work well.
I run multiple nodes started around the same time, on very similar hardware. Some nodes were out of space and being migrated to new drives when eu-north appeared, while others completed the migration earlier. Now the nodes that were out of space are sitting at around 30 audits and almost 0 traffic, while nodes that had space have more than 3000 audits and the data gets uploaded there.
I can’t comment on the status of implementation. But your numbers aren’t that strange. The initial audit is selected in the way described in that document, but auditing that segment also audits up to 79 other nodes. For those 79 pieces it still goes that the more data your node holds, the higher the chance you’re audited.
So out of 80 nodes audited only one was selected with priority. Picking audits where at least one node will be an unvetted node is the best you can do when an audit always audits 80 nodes at the same time.