I never defended this action, however, there is one good reason for this: across millions of these inactive games with <1,000 visits, there are definitely going to be some games with inappropriate content. This is a catch-all method to ensure that those games are neither discovered nor played again.
Adding an 18+ age restriction won’t help because then Roblox still runs the risk of those few games with inappropriate content being played.
Sure, it might only be a few of those games, but it is asinine for anyone to think that Roblox could manually review every single game for inappropriate content (not saying you personally think this, but others that are reading this definitely do).