Simple reason: Today is was thinking about what kind of postings we have in our categories, and while browsing through #site-feedback, I stumbled over some posts that seemed worth getting a bit more attention, so I decided to bump them. Since there is no "Bump" button available for direct action, a timer has to be set, as low as it may be (1min) -> That's then the "automated bump".
I find this automated bump interesting for topics that don't necessarily need to be pinned, but could use some love from time to time. Currently, the "automated" bump is a manual action.
As I learned today, it can be more automated, i.e. every topic that is not solved or otherwise closed will get bumped after a specified time. Topics to be bumped are randomly selected.
I have seen this today on meta.discourse.org and was surprised to find 3 year old topics bumped, for apparently no reason.
I'm not sure if doing this kind of automated bumping would be beneficial for the OpenWrt forum, but if users of the forum show interest in this option, we can certainly think about trying it out.