It would appear that after reading many reports from Facebook Instant Game developers, new games launched are no longer visible to end users at all. Developers are reporting 0 users for the lifetime of their games even though their games have been reviewed and approved by Facebook and are globally launched.
T took a look through the Facebook Instant Games platform dashboard to see what has changed. It appears that the Facebook App platform option has been removed. As developers know, without this option they cannot submit their game for approval by App Centre and appear in the curated Facebook games list. Whilst App Centre is effectively separate from the Facebook Instant games platform, it does however link into it.
It is my opinion that the missing Facebook App option is the cause of the issue. It has either been removed by mistake for new games (its still available for older games) or Facebook are completely killing visibility of all new games, leaving paid adverts as the only option for visibility. I do hope that Facebook have not gone this route as it will push almost every developer in poor countries off the platform.
My advice for now is to not launch your games until Facebook provide an answer or solution to this issue.