Developers just need to ask the mods to be moved to the curated category. The mods then decide if that game is worthy of being put there based on game quality, development status, thread popularity etc.:
For my part I don’t see much use in the category currently, most games get a fraction of the traction that threads in Projects do (only 7 threads have seen any activity in the last month), and it requires a lot of upkeep from the developer to properly make use of the multiple threads per game feature.
The idea of it being a handpicked selection of top-quality games is nice but its numerous flaws are likely a reason why a lot of developers haven’t moved over there. As for archiving them, that’s another thing that the developer has to request, not based on inactivity. You can probably find a dozen different threads explaining why that’s the case.